JZ21：栈的压入、弹出序列

import java.util.Stack;
public class Solution {
  public boolean IsPopOrder(int [] pushA,int [] popA) {
      Stack<Integer> stack=new Stack<Integer>();
      int index=0;
      for(int i=0;i<pushA.length;i++){
          stack.push(pushA[i]);
          while(!stack.isEmpty() && stack.peek()==popA[index]){
              stack.pop();
              index++;
          }
      }
      return stack.isEmpty();
  }
}