Validate Stack Sequences

Description

Given two integer arrays pushed and popped each with distinct values, return true if this could have been the result of a sequence of push and pop operations on an initially empty stack, or false otherwise.

Example 1:

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1] Output: true Explanation: We might do the following sequence: push(1), push(2), push(3), push(4), pop() → 4, push(5), pop() → 5, pop() → 3, pop() → 2, pop() → 1

Example 2:

Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2] Output: false Explanation: 1 cannot be popped before 2.

Constraints:

• 1 <= pushed.length <= 1000
• 0 <= pushed[i] <= 1000
• All the elements of pushed are unique.
• popped.length == pushed.length
• popped is a permutation of pushed.

Code

class Solution {
public:
    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
        stack<int> st;
        int j = 0;
        for(auto p: pushed) {
            st.push(p);
            while(!st.empty() && st.top() == popped[j]) {
                st.pop();
                j++;
            }
        }
 
        return st.empty();
    }
};

Source

• Validate Stack Sequences - LeetCode