LeetCode 946. 验证栈序列(Validate Stack Sequences) 26

946. 验证栈序列

946. Validate Stack Sequences

题目描述

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.

每日一算法2019/5/29Day 26LeetCode946. Validate Stack Sequences

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.

Java 实现

import java.util.Stack;

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        int n = pushed.length;
        Stack<Integer> stack = new Stack<>();
        for (int pushIndex = 0, popIndex = 0; pushIndex < n; pushIndex++) {
            stack.push(pushed[pushIndex]);
            while (popIndex < n && !stack.isEmpty() && stack.peek() == popped[popIndex]) {
                stack.pop();
                popIndex++;
            }
        }
        return stack.isEmpty();
    }
}

参考资料

• https://leetcode-cn.com/problems/validate-stack-sequences/
• https://leetcode.com/problems/validate-stack-sequences/