面试题 31. 栈的压入、弹出序列

输入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
输出：true
解释：我们可以按以下顺序执行：
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

输入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
输出：false
解释：1 不能在 2 之前弹出。

class Solution:
    def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:
        s = []
        q = 0
        for num in pushed:
            s.append(num)
            while s and s[-1] == popped[q]:
                s.pop()
                q += 1
        return not s

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        Deque<Integer> s = new ArrayDeque<>();
        int q = 0;
        for (int num : pushed) {
            s.push(num);
            while (!s.isEmpty() && s.peek() == popped[q]) {
                s.pop();
                ++q;
            }
        }
        return s.isEmpty();
    }
}

/**
 * @param {number[]} pushed
 * @param {number[]} popped
 * @return {boolean}
 */
var validateStackSequences = function (pushed, popped) {
  let s = [];
  let q = 0;
  for (let num of pushed) {
    s.push(num);
    while (s.length > 0 && s[s.length - 1] == popped[q]) {
      ++q;
      s.pop();
    }
  }
  return s.length == 0;
};

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