LeetCode946. 驗證棧序列

946. Validate Stack Sequences

[Medium] Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

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.

Note:

1. 0 <= pushed.length == popped.length <= 1000
2. 0 <= pushed[i], popped[i] < 1000
3. pushed is a permutation of popped.
4. pushed and popped have distinct values.

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題目：給定 pushed 和 popped 兩個序列，每個序列中的 值都不重複，只有當它們可能是在最初空棧上進行的推入 push 和彈出 pop 操作序列的結果時，返回 true；否則，返回 false 。

思路：模擬入棧出棧的過程。

工程代碼下載 Github

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