leetcode946. Validate Stack Sequences

题目链接
题目：给出两个数组，调整第一个数组的输入输出顺序能否变成第二个数组
示例：
输入: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
输出: true
思路：遍历一下，利用栈的属性

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        Stack<Integer> stack = new Stack<Integer>();
        int k = popped.length;
        int j = 0;
        if(k == 0){
            return true;
        }
        for(int i = 0; i < k; i++){
            if(popped[j] == pushed[i]){
                j++;
            }else if(stack.isEmpty()){
                stack.push(pushed[i]);
            }else{
                if(stack.peek() == popped[j]){
                    stack.pop();
                    j++;
                    i--;
                }else{
                    stack.push(pushed[i]);
                }
            }
        }
        while(!stack.isEmpty() && stack.peek() == popped[j]){
            stack.pop();
            j++;
        }

        if(stack.isEmpty() && j == k){
            return true;
        }
        return false;
    }
}

我的代码有点low，看看别人的代码 不过他的代码没我的快点 哈哈哈

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