剑指Offer31-栈的压入、弹出序列

剑指Offer31-栈的压入、弹出序列

输入两个整数序列,第一个序列表示栈的压入顺序,请判断第二个序列是否为该栈的弹出顺序。假设压入栈的所有数字均不相等。例如,序列 {1,2,3,4,5} 是某栈的压栈序列,序列 {4,5,3,2,1} 是该压栈序列对应的一个弹出序列,但 {4,3,5,1,2} 就不可能是该压栈序列的弹出序列。

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. 0 <= pushed.length == popped.length <= 1000

  2. 0 <= pushed[i], popped[i] < 1000

  3. pushed 是 popped 的排列。

来源:力扣(LeetCode)

链接:力扣

一解

使用辅助栈模拟操作,设

  • pushed = [1,2,3,4,5]

  • popped = [4,5,3,2,1]


class Solution:

    def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:

        stack, i = [], 0

        for num in pushed:

            stack.append(num)

            while stack and stack[-1] == popped[i]:

                stack.pop()

                i += 1

        return not stack

def validate_stack(pushed: list, popped: list):
    stack, index = [], 0
    for i in pushed:
        stack.append(i)
        while stack and stack[-1] == popped[index]:
            stack.pop()
            index += 1  # popped如果长度和pushed一样,那么不用担心数组越界
    return not stack


assert validate_stack([1, 2, 3, 4, 5], [4, 5, 3, 2, 1]) is True
assert validate_stack([1, 2, 3, 4, 5], [4, 3, 5, 1, 2]) is False

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