946. 验证栈序列

Difficulty
Medium
Tags
栈
URL
https://leetcode.cn/problems/validate-stack-sequences/
Star
给定 pushed 和 popped 两个序列，每个序列中的 值都不重复，只有当它们可能是在最初空栈上进行的推入 push 和弹出 pop 操作序列的结果时，返回 true；否则，返回 false 。
示例 1：
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
示例 2：
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。
提示：
  • 1 <= pushed.length <= 1000
  • 0 <= pushed[i] <= 1000
  • pushed 的所有元素 互不相同
  • popped.length == pushed.length
  • popped 是 pushed 的一个排列
通过次数64,057提交次数96,142

用栈模拟

思路
建立一个stack来模拟入栈出栈的过程
题解
class Solution:
    def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:
        stack = []
        p2 = 0
        for i in range(0, len(pushed)):
            stack.append(pushed[i])
            while stack and p2 < len(popped) and stack[-1] == popped[p2]:
                p2 += 1
                stack.pop()

        return p2 == len(popped)

虚拟栈模拟

思路
定义两个指针，p1指向入栈顶，p2指向出栈的顺序。
题解
class Solution:
    def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:

        p2 = 0 # 指向 popped
        p1 = 0 # 指向 pushed 栈顶
        for i in range(0, len(pushed)):
            pushed[p1] = pushed[i]
            while p1 >= 0 and p2 < len(popped) and pushed[p1] == popped[p2]:
                p2 += 1
                p1 -= 1
            p1 += 1

        return p2 == len(popped)