Minimum Prefix Removal to Make Array Strictly Increasing Python/Java solution

The typical implementation performs a reverse loop starting from the last index and moves left while nums[i-1] < nums[i]. Once the condition fails, return the current index as the number of elements to remove. The same logic works in Python, Java, C++, Go, and TypeScript with O(n) time and constant space.

What is the best approach for Minimum Prefix Removal to Make Array Strictly Increasing?

Reverse traversal is the most efficient approach. Scan from the end of the array and find the longest strictly increasing suffix where nums[i-1] < nums[i]. The index where this property first breaks determines how many prefix elements must be removed. This runs in O(n) time and O(1) space.

Is Minimum Prefix Removal to Make Array Strictly Increasing asked at Google/Amazon/Meta?

Problems involving strictly increasing subarrays, suffix scans, and array order validation frequently appear in interviews at companies like Amazon, Google, and Meta. Variants of this problem test whether candidates can identify monotonic segments and optimize from brute force to a linear scan.

What data structure is used in Minimum Prefix Removal to Make Array Strictly Increasing?

The solution operates directly on arrays. No additional data structures such as hash maps or stacks are required because the property of strict ordering can be verified by comparing adjacent elements during a single traversal.

What is the time complexity of Minimum Prefix Removal to Make Array Strictly Increasing?

The optimal solution runs in O(n) time because the array is scanned once from right to left. Each element is checked against its neighbor to verify the strictly increasing condition. Space complexity is O(1) since the algorithm only uses a few variables.

Description Hints 2 Solution Video 4:52

3818. Minimum Prefix Removal to Make Array Strictly Increasing

Q: Is Minimum Prefix Removal to Make Array Strictly Increasing easy or hard?

The problem is usually classified as Medium difficulty. The brute force idea is straightforward, but identifying that the answer depends on the longest strictly increasing suffix requires recognizing a pattern that leads to the optimal O(n) solution.

Q: How to solve Minimum Prefix Removal to Make Array Strictly Increasing in O(n)?

Traverse the array from the last element toward the beginning while the strictly increasing condition nums[i-1] < nums[i] holds. Stop when a violation appears. The suffix starting at that position is already strictly increasing, so removing the prefix up to that index produces the valid result. The traversal touches each element once, giving O(n) time.

Q: What is the best approach for Minimum Prefix Removal to Make Array Strictly Increasing?

Reverse traversal is the most efficient approach. Scan from the end of the array and find the longest strictly increasing suffix where nums[i-1] < nums[i]. The index where this property first breaks determines how many prefix elements must be removed. This runs in O(n) time and O(1) space.

Q: Is Minimum Prefix Removal to Make Array Strictly Increasing asked at Google/Amazon/Meta?

Problems involving strictly increasing subarrays, suffix scans, and array order validation frequently appear in interviews at companies like Amazon, Google, and Meta. Variants of this problem test whether candidates can identify monotonic segments and optimize from brute force to a linear scan.

Q: What data structure is used in Minimum Prefix Removal to Make Array Strictly Increasing?

The solution operates directly on arrays. No additional data structures such as hash maps or stacks are required because the property of strict ordering can be verified by comparing adjacent elements during a single traversal.

Q: What is the time complexity of Minimum Prefix Removal to Make Array Strictly Increasing?

The optimal solution runs in O(n) time because the array is scanned once from right to left. Each element is checked against its neighbor to verify the strictly increasing condition. Space complexity is O(1) since the algorithm only uses a few variables.

Medium73.7% acceptance1 company

You are given an integer array nums.

You need to remove exactly one prefix (possibly empty) from nums.

Return an integer denoting the minimum length of the removed prefix such that the remaining array is strictly increasing.

Example 1:

Input: nums = [1,-1,2,3,3,4,5]

Output: 4

Explanation:

Removing the prefix = [1, -1, 2, 3] leaves the remaining array [3, 4, 5] which is strictly increasing.

Example 2:

Input: nums = [4,3,-2,-5]

Output: 3

Explanation:

Removing the prefix = [4, 3, -2] leaves the remaining array [-5] which is strictly increasing.

Example 3:

Input: nums = [1,2,3,4]

Output: 0

Explanation:

The array nums = [1, 2, 3, 4] is already strictly increasing so removing an empty prefix is sufficient.

Constraints:

1 <= nums.length <= 10⁵
-10⁹ <= nums[i] <= 10⁹

Asked at 1 company

JPMorgan Chase

Topics

Array

Hints open one at a time

Hint 1

Find the first index i from the right such that nums[i] >= nums[i + 1].

Hint 2

If such an index exists, the answer is i + 1; otherwise, the array is already strictly increasing.

4:52

Still stuck?Read the written solution, or watch a walkthrough.

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1class Solution:
2    def minimumPrefixLength(self, nums: List[int]) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1Case 2Case 3

Input

[1,-1,2,3,3,4,5]

Input

[4,3,-2,-5]

Input

[1,2,3,4]

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