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The key idea is to use a stack to simulate the push and pop operations. We iterate over each element in the pushed array, pushing them onto the stack. After each push, we check the top of the stack to see if it matches the next element in the popped array. If it does, we pop the stack. By the end of both arrays, if all operations are valid, the stack should be empty.
Time Complexity: O(n), where n is the number of elements in the array.
Space Complexity: O(n), for the stack storage used during the process.
1#include <stdbool.h>
2
3bool validateStackSequences(int* pushed, int pushedSize, int* popped, int poppedSize) {
4 int stack[pushedSize];
5 int top = -1, j = 0;
6 for (int i = 0; i < pushedSize; i++) {
7 stack[++top] = pushed[i]; // Push operation
8 while (top >= 0 && stack[top] == popped[j]) { // Check if top of stack equals next popped value
9 top--;
10 j++;
11 }
12 }
13 return top == -1;
14}This C solution initializes a stack and iterates through the pushed array. For each element, it checks if the stack's top element matches the next element in the popped array. If so, it pops the stack. Finally, it returns true if all elements were correctly popped, indicated by an empty stack.
In this approach, you can use two pointers to bypass the use of an explicit stack. You iterate over the pushed array with one pointer while another pointer operates over the popped array. Match elements and mimic stack operations conceptually.
Time Complexity: O(n), where n is the length of the arrays.
Space Complexity: O(1), as no extra space is used aside from input arrays.
1functionThe JavaScript version carries forward the reuse of the input array to serve as stack space using pointer variables. It directly modifies and checks values to guarantee correctness of given sequences.