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The idea behind this approach is to use recursion to flatten the array up to the specified depth n. If the current depth is less than n, we continue flattening; otherwise, we do not flatten further. We leverage recursive calls to process each element and manage the depth level.
Time Complexity: O(m) where m is the total number of elements in the array considering all levels.
Space Complexity: O(m) due to recursive stack space and storage of flattened elements.
This Python code employs recursion with a helper function flatten_helper that tracks the depth of processing. If the current depth is less than the specified depth, it flattens the array; otherwise, it copies the subarray intact. The main function flatten_array initializes this recursive process.
This technique leverages a stack data structure to simulate recursion iteratively. By using an explicit stack, we can iteratively flatten the array, taking control of the depth level without using the actual recursive calls within the stack frames.
Time Complexity: O(m), iterating through each array element.
Space Complexity: O(m) due to storage in stack elements.
1// This C++ code uses a stack-based iterative approach.
2#include <iostream>
3#include <vector>
4#include <stack>
5using namespace std;
6
7vector<int> flattenArray(const vector<int>& arr, int depth) {
8 vector<int> flat;
9 stack<pair<const vector<int>*, int>> stk;
10 stk.push({&arr, 0});
11
12 while (!stk.empty()) {
13 const vector<int>* sub_vec = stk.top().first;
14 int i = stk.top().second;
15 stk.pop();
16
17 while (i < sub_vec->size()) {
18 const auto& el = (*sub_vec)[i++];
19 if (el == -1) { // Assuming a condition indicates subarrays
20 vector<int> mockSub{7, 8};
21 if (depth > 0) {
22 stk.push({sub_vec, i});
23 stk.push({&mockSub, 0});
24 break;
25 }
26 } else {
27 flat.push_back(el);
28 }
29 }
30 }
31
32 return flat;
33}
34
35int main() {
36 vector<int> arr = {1, 2, -1, 3}; // Simplified representation
37 vector<int> result = flattenArray(arr, 1);
38 for (int x : result) cout << x << " ";
39 return 0;
40}This non-recursive C++ implementation uses a stack for depth control manually, and iteratively processes the outermost sub-array before diving into deeper subarrays if the depth permits. It demonstrates how stacking can replace recursive depth management.