946. Validate Stack Sequences

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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.

🧠 Thuật Toán & Kỹ Thuật

Stack (Ngăn xếp)
⏱️ Thời gian O(n)
💾 Không gian O(n)

💻 Lời Giải

C++ 0946-validate-stack-sequences.cpp 
class Solution {
public:
    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
        stack<int> st;
        int j = 0;
        const int n = popped.size();
        
        for (int num : pushed) {
            st.push(num);
            while (!st.empty() and j < n and st.top() == popped[j]) {
                st.pop(), j++;
            }
        }
        
        return j == n;
    }
};