stack push and pop sequence
Question:
Input two sequences of integers. The first sequence represents the push sequence of the stack. Please judge whether the second sequence may be the pop-up sequence of the stack. Assume that all numbers pushed onto the stack are not equal. For example, the sequence 1, 2, 3, 4, 5 is the push sequence of a stack, the sequence 4, 5, 3, 2, 1 is a pop sequence corresponding to the stack sequence, but 4, 3, 5, 1, 2 It cannot be the pop sequence of the push sequence. (Note: the lengths of these two sequences are equal)
Code:
package com.sjsq.test;
import java.util.Stack;
/**
* @author shuijianshiqing
* @date 2020/5/23 20:06
*/
/**
* 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
* 序列是否可能为该栈的弹出顺序。假设压入栈的所有数字均不相等。
* 例如序列1,2,3,4,5是某栈的压入顺序，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。（注意：这两个序列的长度是相等的）
*/
public class Solution {
public boolean IsPopOrder(int [] pushA,int [] popA) {
if(pushA.length == 0 || popA.length == 0 || popA.length != pushA.length){
return false;
}
Stack<Integer> stack = new Stack<Integer>();
int j = 0;
for(int i = 0; i < pushA.length; i++){
stack.push(pushA[i]);
while(!stack.isEmpty() && stack.peek() == popA[j]){
stack.pop();
j++;
}
}
return stack.isEmpty();
}
}