Minimum Absolute Difference Between Elements With Constraint solution and explanation
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The problem
You are given a 0-indexed integer array nums and an integer x.
Find the minimum absolute difference between two elements in the array that are at least x indices apart.
In other words, find two indices i and j such that abs(i - j) >= x and abs(nums[i] - nums[j]) is minimized.
Return an integer denoting the minimum absolute difference between two elements that are at least x indices apart.
Example 1:
Input: nums = [4,3,2,4], x = 2 Output: 0 Explanation: We can select nums[0] = 4 and nums[3] = 4. They are at least 2 indices apart, and their absolute difference is the minimum, 0. It can be shown that 0 is the optimal answer.
Example 2:
Input: nums = [5,3,2,10,15], x = 1 Output: 1 Explanation: We can select nums[1] = 3 and nums[2] = 2. They are at least 1 index apart, and their absolute difference is the minimum, 1. It can be shown that 1 is the optimal answer.
Example 3:
Input: nums = [1,2,3,4], x = 3 Output: 3 Explanation: We can select nums[0] = 1 and nums[3] = 4. They are at least 3 indices apart, and their absolute difference is the minimum, 3. It can be shown that 3 is the optimal answer.
Constraints:
1 <= nums.length <= 1051 <= nums[i] <= 1090 <= x < nums.length
Approach overview
Problem Overview: You are given an integer array nums and an integer x. The goal is to find the minimum absolute difference between two elements nums[i] and nums[j] such that |i - j| ≥ x. The constraint prevents comparing nearby elements, so the algorithm must track only values that are far enough apart in the array.
Approach 1: Brute Force with Constraint Check (O(n²) time, O(1) space)
The straightforward approach checks every valid pair. Iterate through the array using two nested loops and only evaluate pairs where |i - j| ≥ x. For each valid pair, compute abs(nums[i] - nums[j]) and track the minimum. This method is simple and clearly demonstrates the constraint logic, but it performs up to n² comparisons and becomes impractical for large inputs.
Approach 2: Sliding Window with Sorted List (O(n log n) time, O(n) space)
The optimized approach maintains a dynamically sorted structure of eligible elements. As you iterate through the array, add the element nums[i - x] into an ordered structure once it becomes valid for comparison. This ensures every stored value satisfies the index distance constraint.
Use an ordered set or sorted list and locate the closest values to nums[i] using binary search. Specifically, find the first element greater than or equal to nums[i] and also check the previous element. These two candidates produce the smallest possible absolute difference in a sorted structure. Update the global minimum after each comparison.
The key insight: in a sorted structure, the nearest values to a number must lie directly adjacent in order. Binary search finds those candidates in O(log n), and insertion also costs O(log n) for balanced trees (or O(n) in Python lists but still efficient in practice). Iterating once through the array results in overall O(n log n) time.
Recommended for interviews: Start with the brute force idea to show you understand the constraint and pair comparison logic. Then move to the ordered-set solution. Interviewers typically expect the O(n log n) approach using a balanced tree, TreeSet, or sorted container because it demonstrates knowledge of binary search on dynamic data structures.
Approach 1: Sliding Window with Sorted List
from sortedcontainers import SortedList
def minAbsoluteDifference(nums, x):
n = len(nums)
sorted_list = SortedList()
min_diff = float('inf')
for i in range(n):
if i >= x:
sorted_list.add(nums[i-x])
if sorted_list:
idx = sorted_list.bisect_left(nums[i])
if idx < len(sorted_list):
min_diff = min(min_diff, abs(sorted_list[idx] - nums[i]))
if idx > 0:
min_diff = min(min_diff, abs(sorted_list[idx-1] - nums[i]))
return min_diffimport java.util.*;
public class Solution {
public int minAbsoluteDifference(int[] nums, int x) {
TreeSet<Integer> sortedSet = new TreeSet<>();
int minDiff = Integer.MAX_VALUE;
for (int i = 0; i < nums.length; i++) {
if (i >= x) {
sortedSet.add(nums[i - x]);
}
if (!sortedSet.isEmpty()) {
Integer higher = sortedSet.ceiling(nums[i]);
Integer lower = sortedSet.floor(nums[i]);
if (higher != null) {
minDiff = Math.min(minDiff, Math.abs(higher - nums[i]));
}
if (lower != null) {
minDiff = Math.min(minDiff, Math.abs(lower - nums[i]));
}
}
}
return minDiff;
}
}#include <set>
#include <vector>
#include <algorithm>
#include <cmath>
int minAbsoluteDifference(std::vector<int>& nums, int x) {
std::multiset<int> sortedSet;
int minDiff = INT_MAX;
for (int i = 0; i < nums.size(); ++i) {
if (i >= x) {
sortedSet.insert(nums[i-x]);
}
if (!sortedSet.empty()) {
auto it = sortedSet.lower_bound(nums[i]);
if (it != sortedSet.end()) {
minDiff = std::min(minDiff, std::abs(*it - nums[i]));
}
if (it != sortedSet.begin()) {
--it;
minDiff = std::min(minDiff, std::abs(*it - nums[i]));
}
}
}
return minDiff;
}function minAbsoluteDifference(nums, x) {
const sortedList = new Set();
let minDiff = Infinity;
function insertSorted(num) {
sortedList.add(num);
sortedList = new Set(Array.from(sortedList).sort((a, b) => a - b));
}
for (let i = 0; i < nums.length; i++) {
if (i >= x) {
insertSorted(nums[i - x]);
}
if (sortedList.size > 0) {
const sortedArr = Array.from(sortedList);
const idx = sortedArr.findIndex(v => v >= nums[i]);
if (idx < sortedArr.length) {
minDiff = Math.min(minDiff, Math.abs(sortedArr[idx] - nums[i]));
}
if (idx > 0) {
minDiff = Math.min(minDiff, Math.abs(sortedArr[idx - 1] - nums[i]));
}
}
}
return minDiff;
}using System;
using System.Collections.Generic;
public class Solution {
public int MinAbsoluteDifference(int[] nums, int x) {
SortedSet<int> sortedSet = new SortedSet<int>();
int minDiff = int.MaxValue;
for (int i = 0; i < nums.Length; i++) {
if (i >= x) {
sortedSet.Add(nums[i - x]);
}
if (sortedSet.Count > 0) {
int? lower = sortedSet.GetViewBetween(int.MinValue, nums[i]).Max;
int? higher = sortedSet.GetViewBetween(nums[i], int.MaxValue).Min;
if (higher.HasValue) {
minDiff = Math.Min(minDiff, Math.Abs(higher.Value - nums[i]));
}
if (lower.HasValue) {
minDiff = Math.Min(minDiff, Math.Abs(lower.Value - nums[i]));
}
}
}
return minDiff;
}
}This solution uses the SortedList from the 'sortedcontainers' module for efficient insertion and access. As we iterate over elements in 'nums', we maintain a sliding window of the last 'x' elements in sorted order. For each element, we check adjacent elements from the sorted list to find the minimum difference and update our result.
Time Complexity: O(n log x), where n is the length of the array and x is the constraint for indices apart. Space Complexity: O(x) due to storing the elements in the sorted list.
Approach 2: Brute Force with Constraint Check
def minAbsoluteDifference(nums, x):
min_diff = float('inf')
n = len(nums)
for i in range(n):
for j in range(i + x, n):
min_diff = min(min_diff, abs(nums[i] - nums[j]))
return min_diffpublic class Solution {
public int minAbsoluteDifference(int[] nums, int x) {
int minDiff = Integer.MAX_VALUE;
for (int i = 0; i < nums.length; i++) {
for (int j = i + x; j < nums.length; j++) {
minDiff = Math.min(minDiff, Math.abs(nums[i] - nums[j]));
}
}
return minDiff;
}
}#include <vector>
#include <algorithm>
#include <cstdlib>
int minAbsoluteDifference(std::vector<int>& nums, int x) {
int minDiff = INT_MAX;
for (int i = 0; i < nums.size(); ++i) {
for (int j = i + x; j < nums.size(); ++j) {
minDiff = std::min(minDiff, std::abs(nums[i] - nums[j]));
}
}
return minDiff;
}function minAbsoluteDifference(nums, x) {
let minDiff = Infinity;
for (let i = 0; i < nums.length; i++) {
for (let j = i + x; j < nums.length; j++) {
minDiff = Math.min(minDiff, Math.abs(nums[i] - nums[j]));
}
}
return minDiff;
}public class Solution {
public int MinAbsoluteDifference(int[] nums, int x) {
int minDiff = int.MaxValue;
for (int i = 0; i < nums.Length; i++) {
for (int j = i + x; j < nums.Length; j++) {
minDiff = Math.Min(minDiff, Math.Abs(nums[i] - nums[j]));
}
}
return minDiff;
}
}This Python code loops through each permissible pair, checks if their index difference meets the constraint and calculates the absolute difference to find the minimum.
Time Complexity: O(n^2), as all pairs are checked. Space Complexity: O(1), as only simple variables are used.
Approach 3: Ordered Set
We create an ordered set to store the elements whose distance to the current index is at least x.
Next, we enumerate from index i = x, each time we add nums[i - x] into the ordered set. Then we find the two elements in the ordered set which are closest to nums[i], and the minimum absolute difference between them is the answer.
The time complexity is O(n times log n), and the space complexity is O(n). Where n is the length of array nums.
function minAbsoluteDifference(nums: number[], x: number): number {
const s = new TreeMultiSet<number>();
const inf = 1 << 30;
let ans = inf;
for (let i = x; i < nums.length; ++i) {
s.add(nums[i - x]);
const c = s.ceil(nums[i]);
const f = s.floor(nums[i]);
if (c) {
ans = Math.min(ans, c - nums[i]);
}
if (f) {
ans = Math.min(ans, nums[i] - f);
}
}
return ans;
}
type Compare<T> = (lhs: T, rhs: T) => number;
class RBTreeNode<T = number> {
data: T;
count: number;
left: RBTreeNode<T> | null;
right: RBTreeNode<T> | null;
parent: RBTreeNode<T> | null;
color: number;
constructor(data: T) {
this.data = data;
this.left = this.right = this.parent = null;
this.color = 0;
this.count = 1;
}
sibling(): RBTreeNode<T> | null {
if (!this.parent) return null; // sibling null if no parent
return this.isOnLeft() ? this.parent.right : this.parent.left;
}
isOnLeft(): boolean {
return this === this.parent!.left;
}
hasRedChild(): boolean {
return (
Boolean(this.left && this.left.color === 0) ||
Boolean(this.right && this.right.color === 0)
);
}
}
class RBTree<T> {
root: RBTreeNode<T> | null;
lt: (l: T, r: T) => boolean;
constructor(compare: Compare<T> = (l: T, r: T) => (l < r ? -1 : l > r ? 1 : 0)) {
this.root = null;
this.lt = (l: T, r: T) => compare(l, r) < 0;
}
rotateLeft(pt: RBTreeNode<T>): void {
const right = pt.right!;
pt.right = right.left;
if (pt.right) pt.right.parent = pt;
right.parent = pt.parent;
if (!pt.parent) this.root = right;
else if (pt === pt.parent.left) pt.parent.left = right;
else pt.parent.right = right;
right.left = pt;
pt.parent = right;
}
rotateRight(pt: RBTreeNode<T>): void {
const left = pt.left!;
pt.left = left.right;
if (pt.left) pt.left.parent = pt;
left.parent = pt.parent;
if (!pt.parent) this.root = left;
else if (pt === pt.parent.left) pt.parent.left = left;
else pt.parent.right = left;
left.right = pt;
pt.parent = left;
}
swapColor(p1: RBTreeNode<T>, p2: RBTreeNode<T>): void {
const tmp = p1.color;
p1.color = p2.color;
p2.color = tmp;
}
swapData(p1: RBTreeNode<T>, p2: RBTreeNode<T>): void {
const tmp = p1.data;
p1.data = p2.data;
p2.data = tmp;
}
fixAfterInsert(pt: RBTreeNode<T>): void {
let parent = null;
let grandParent = null;
while (pt !== this.root && pt.color !== 1 && pt.parent?.color === 0) {
parent = pt.parent;
grandParent = pt.parent.parent;
/* Case : A
Parent of pt is left child of Grand-parent of pt */
if (parent === grandParent?.left) {
const uncle = grandParent.right;
/* Case : 1
The uncle of pt is also red
Only Recoloring required */
if (uncle && uncle.color === 0) {
grandParent.color = 0;
parent.color = 1;
uncle.color = 1;
pt = grandParent;
} else {
/* Case : 2
pt is right child of its parent
Left-rotation required */
if (pt === parent.right) {
this.rotateLeft(parent);
pt = parent;
parent = pt.parent;
}
/* Case : 3
pt is left child of its parent
Right-rotation required */
this.rotateRight(grandParent);
this.swapColor(parent!, grandParent);
pt = parent!;
}
} else {
/* Case : B
Parent of pt is right child of Grand-parent of pt */
const uncle = grandParent!.left;
/* Case : 1
The uncle of pt is also red
Only Recoloring required */
if (uncle != null && uncle.color === 0) {
grandParent!.color = 0;
parent.color = 1;
uncle.color = 1;
pt = grandParent!;
} else {
/* Case : 2
pt is left child of its parent
Right-rotation required */
if (pt === parent.left) {
this.rotateRight(parent);
pt = parent;
parent = pt.parent;
}
/* Case : 3
pt is right child of its parent
Left-rotation required */
this.rotateLeft(grandParent!);
this.swapColor(parent!, grandParent!);
pt = parent!;
}
}
}
this.root!.color = 1;
}
delete(val: T): boolean {
const node = this.find(val);
if (!node) return false;
node.count--;
if (!node.count) this.deleteNode(node);
return true;
}
deleteAll(val: T): boolean {
const node = this.find(val);
if (!node) return false;
this.deleteNode(node);
return true;
}
deleteNode(v: RBTreeNode<T>): void {
const u = BSTreplace(v);
// True when u and v are both black
const uvBlack = (u === null || u.color === 1) && v.color === 1;
const parent = v.parent!;
if (!u) {
// u is null therefore v is leaf
if (v === this.root) this.root = null;
// v is root, making root null
else {
if (uvBlack) {
// u and v both black
// v is leaf, fix double black at v
this.fixDoubleBlack(v);
} else {
// u or v is red
if (v.sibling()) {
// sibling is not null, make it red"
v.sibling()!.color = 0;
}
}
// delete v from the tree
if (v.isOnLeft()) parent.left = null;
else parent.right = null;
}
return;
}
if (!v.left || !v.right) {
// v has 1 child
if (v === this.root) {
// v is root, assign the value of u to v, and delete u
v.data = u.data;
v.left = v.right = null;
} else {
// Detach v from tree and move u up
if (v.isOnLeft()) parent.left = u;
else parent.right = u;
u.parent = parent;
if (uvBlack) this.fixDoubleBlack(u);
// u and v both black, fix double black at u
else u.color = 1; // u or v red, color u black
}
return;
}
// v has 2 children, swap data with successor and recurse
this.swapData(u, v);
this.deleteNode(u);
// find node that replaces a deleted node in BST
function BSTreplace(x: RBTreeNode<T>): RBTreeNode<T> | null {
// when node have 2 children
if (x.left && x.right) return successor(x.right);
// when leaf
if (!x.left && !x.right) return null;
// when single child
return x.left ?? x.right;
}
// find node that do not have a left child
// in the subtree of the given node
function successor(x: RBTreeNode<T>): RBTreeNode<T> {
let temp = x;
while (temp.left) temp = temp.left;
return temp;
}
}
fixDoubleBlack(x: RBTreeNode<T>): void {
if (x === this.root) return; // Reached root
const sibling = x.sibling();
const parent = x.parent!;
if (!sibling) {
// No sibiling, double black pushed up
this.fixDoubleBlack(parent);
} else {
if (sibling.color === 0) {
// Sibling red
parent.color = 0;
sibling.color = 1;
if (sibling.isOnLeft()) this.rotateRight(parent);
// left case
else this.rotateLeft(parent); // right case
this.fixDoubleBlack(x);
} else {
// Sibling black
if (sibling.hasRedChild()) {
// at least 1 red children
if (sibling.left && sibling.left.color === 0) {
if (sibling.isOnLeft()) {
// left left
sibling.left.color = sibling.color;
sibling.color = parent.color;
this.rotateRight(parent);
} else {
// right left
sibling.left.color = parent.color;
this.rotateRight(sibling);
this.rotateLeft(parent);
}
} else {
if (sibling.isOnLeft()) {
// left right
sibling.right!.color = parent.color;
this.rotateLeft(sibling);
this.rotateRight(parent);
} else {
// right right
sibling.right!.color = sibling.color;
sibling.color = parent.color;
this.rotateLeft(parent);
}
}
parent.color = 1;
} else {
// 2 black children
sibling.color = 0;
if (parent.color === 1) this.fixDoubleBlack(parent);
else parent.color = 1;
}
}
}
}
insert(data: T): boolean {
// search for a position to insert
let parent = this.root;
while (parent) {
if (this.lt(data, parent.data)) {
if (!parent.left) break;
else parent = parent.left;
} else if (this.lt(parent.data, data)) {
if (!parent.right) break;
else parent = parent.right;
} else break;
}
// insert node into parent
const node = new RBTreeNode(data);
if (!parent) this.root = node;
else if (this.lt(node.data, parent.data)) parent.left = node;
else if (this.lt(parent.data, node.data)) parent.right = node;
else {
parent.count++;
return false;
}
node.parent = parent;
this.fixAfterInsert(node);
return true;
}
find(data: T): RBTreeNode<T> | null {
let p = this.root;
while (p) {
if (this.lt(data, p.data)) {
p = p.left;
} else if (this.lt(p.data, data)) {
p = p.right;
} else break;
}
return p ?? null;
}
*inOrder(root: RBTreeNode<T> = this.root!): Generator<T, undefined, void> {
if (!root) return;
for (const v of this.inOrder(root.left!)) yield v;
yield root.data;
for (const v of this.inOrder(root.right!)) yield v;
}
*reverseInOrder(root: RBTreeNode<T> = this.root!): Generator<T, undefined, void> {
if (!root) return;
for (const v of this.reverseInOrder(root.right!)) yield v;
yield root.data;
for (const v of this.reverseInOrder(root.left!)) yield v;
}
}
class TreeMultiSet<T = number> {
_size: number;
tree: RBTree<T>;
compare: Compare<T>;
constructor(
collection: T[] | Compare<T> = [],
compare: Compare<T> = (l: T, r: T) => (l < r ? -1 : l > r ? 1 : 0),
) {
if (typeof collection === 'function') {
compare = collection;
collection = [];
}
this._size = 0;
this.compare = compare;
this.tree = new RBTree(compare);
for (const val of collection) this.add(val);
}
size(): number {
return this._size;
}
has(val: T): boolean {
return !!this.tree.find(val);
}
add(val: T): boolean {
const successful = this.tree.insert(val);
this._size++;
return successful;
}
delete(val: T): boolean {
const successful = this.tree.delete(val);
if (!successful) return false;
this._size--;
return true;
}
count(val: T): number {
const node = this.tree.find(val);
return node ? node.count : 0;
}
ceil(val: T): T | undefined {
let p = this.tree.root;
let higher = null;
while (p) {
if (this.compare(p.data, val) >= 0) {
higher = p;
p = p.left;
} else {
p = p.right;
}
}
return higher?.data;
}
floor(val: T): T | undefined {
let p = this.tree.root;
let lower = null;
while (p) {
if (this.compare(val, p.data) >= 0) {
lower = p;
p = p.right;
} else {
p = p.left;
}
}
return lower?.data;
}
higher(val: T): T | undefined {
let p = this.tree.root;
let higher = null;
while (p) {
if (this.compare(val, p.data) < 0) {
higher = p;
p = p.left;
} else {
p = p.right;
}
}
return higher?.data;
}
lower(val: T): T | undefined {
let p = this.tree.root;
let lower = null;
while (p) {
if (this.compare(p.data, val) < 0) {
lower = p;
p = p.right;
} else {
p = p.left;
}
}
return lower?.data;
}
first(): T | undefined {
return this.tree.inOrder().next().value;
}
last(): T | undefined {
return this.tree.reverseInOrder().next().value;
}
shift(): T | undefined {
const first = this.first();
if (first === undefined) return undefined;
this.delete(first);
return first;
}
pop(): T | undefined {
const last = this.last();
if (last === undefined) return undefined;
this.delete(last);
return last;
}
*[Symbol.iterator](): Generator<T, void, void> {
yield* this.values();
}
*keys(): Generator<T, void, void> {
for (const val of this.values()) yield val;
}
*values(): Generator<T, undefined, void> {
for (const val of this.tree.inOrder()) {
let count = this.count(val);
while (count--) yield val;
}
return undefined;
}
/**
* Return a generator for reverse order traversing the multi-set
*/
*rvalues(): Generator<T, undefined, void> {
for (const val of this.tree.reverseInOrder()) {
let count = this.count(val);
while (count--) yield val;
}
return undefined;
}
}func minAbsoluteDifference(nums []int, x int) int {
rbt := redblacktree.NewWithIntComparator()
ans := 1 << 30
for i := x; i < len(nums); i++ {
rbt.Put(nums[i-x], nil)
c, _ := rbt.Ceiling(nums[i])
f, _ := rbt.Floor(nums[i])
if c != nil {
ans = min(ans, c.Key.(int)-nums[i])
}
if f != nil {
ans = min(ans, nums[i]-f.Key.(int))
}
}
return ans
}Complexity comparison
| Approach | Complexity |
|---|---|
| Sliding Window with Sorted List | Time Complexity: O(n log x), where n is the length of the array and x is the constraint for indices apart. Space Complexity: O(x) due to storing the elements in the sorted list. |
| Brute Force with Constraint Check | Time Complexity: O(n^2), as all pairs are checked. Space Complexity: O(1), as only simple variables are used. |
| Ordered Set | – |
Complexity analysis
| Approach | Time | Space | When to Use |
|---|---|---|---|
| Brute Force with Constraint Check | O(n²) | O(1) | Good for understanding the constraint logic or very small arrays |
| Sliding Window with Sorted List / Ordered Set | O(n log n) | O(n) | Best general solution; efficient for large inputs and typical interview expectations |
Frequently asked questions
Is Minimum Absolute Difference Between Elements With Constraint easy or hard?
The problem is rated Medium on LeetCode because the brute force idea is simple but inefficient. The challenge is recognizing that a dynamically maintained sorted structure enables fast nearest-value queries while respecting the index distance constraint.
Minimum Absolute Difference Between Elements With Constraint Python/Java solution
In Python, a sorted list with the bisect module can maintain ordered elements and perform binary search for neighbors. In Java, TreeSet provides built-in methods like ceiling() and floor() to quickly locate the closest values. Both implementations run in O(n log n) time.
How to solve Minimum Absolute Difference Between Elements With Constraint in O(n)?
A strict O(n) solution is generally not feasible because you must maintain ordering to find the closest numeric value efficiently. Most optimal implementations rely on a balanced tree, TreeSet, or sorted container with binary search, resulting in O(n log n) time.
What is the best approach for Minimum Absolute Difference Between Elements With Constraint?
The most efficient approach uses a sliding window with an ordered set or sorted list. While iterating through the array, insert elements that are at least x indices behind the current index. Use binary search to find the closest values to the current number in O(log n). This produces an overall time complexity of O(n log n) with O(n) space.
Is Minimum Absolute Difference Between Elements With Constraint asked at Google/Amazon/Meta?
Problems combining ordered sets, binary search, and sliding window techniques commonly appear in interviews at companies like Google, Amazon, and Meta. This question tests the ability to maintain a dynamically sorted structure while enforcing index constraints.
What data structure is used in Minimum Absolute Difference Between Elements With Constraint?
The optimal solution uses an ordered set or balanced binary search tree. Examples include TreeSet in Java, multiset in C++, or a sorted list with bisect in Python. These structures allow efficient insertion and nearest-value lookup using binary search.
What is the time complexity of Minimum Absolute Difference Between Elements With Constraint?
The brute force method runs in O(n²) time because it compares all valid pairs that satisfy the index constraint. The optimized ordered-set approach reduces the complexity to O(n log n) by maintaining a sorted structure and using binary search to find the closest values efficiently.
