借助栈，边push边pop

public boolean IsPopOrder(int [] pushA,int [] popA) {
        if(pushA.length!=popA.length)return false;
        Deque st = new LinkedList();
        int j=0;
        for(int i=0;i<pushA.length;i++){
            while(j<pushA.length&&(st.isEmpty()||st.peek()!=popA[i])){
                st.push(pushA[j]);
                j++;
            }//当栈顶等于pop或者遍历完push都没找到pop元素时结束while循环
            if(st.peek()==popA[i]){
                st.pop();
            }else{
                return false;//说明push里没有pop[i]
            }
        }
        return true;