946. Validate Stack Sequences

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# 題目敘述

Given two integer arrays pushed and popped each with distinct values, return true if this could have been the result of a sequence of push and pop operations on an initially empty stack, or false otherwise.

# 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.

# 解題思路

# Solution

import java.util.Stack;

class Solution {

    public boolean validateStackSequences(int[] pushed, int[] popped) {

        Stack<Integer> stack = new Stack<>();

        int index = 0;

        for(int p : pushed){

            stack.push(p);

            while(!stack.isEmpty() && stack.peek() == popped[index]){

                stack.pop();

                index++;

            }

        }

        return stack.isEmpty();

    }

}