栈的压入、弹出序列_21

题目描述

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 IsPopOrder_21 {
    public boolean IsPopOrder(int [] pushA,int [] popA) {
        if (pushA.length == 0 || popA.length == 0 || pushA.length != popA.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();
    }

    public static void main(String[] args) {
        int [] pushA = {1,2,3,4,5};
        int [] popA = {4,5,3,2,1};
        int [] popB = {4,3,5,1,2};
        IsPopOrder_21 isPopOrder_21 = new IsPopOrder_21();
        boolean b1 = isPopOrder_21.IsPopOrder(pushA, popA);
        System.out.println(b1);
        boolean b2 = isPopOrder_21.IsPopOrder(pushA, popB);
        System.out.println(b2);
    }
}