当前位置 博文首页 > 任萌新的小生活:leetcode232. 用栈实现队列
思路:用两个栈即可完美实现队列,因为栈a元素都倒到栈b,则栈b就是先进后出的队列顺序,当输出是输出输出栈b的栈顶,当输入时,则押入输入栈a,当b内没元素时,就把a中元素都倒入b,当a、b都空时即以为该队列为空。
class MyQueue {
//定义两个栈,一个为输入栈,一个为输出栈
Stack<Integer> a;
Stack<Integer> b;
/** Initialize your data structure here. */
public MyQueue() {
//初始化
a=new Stack<>();
b=new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
//放到输入栈内
a.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
//如果输出栈为空,则把输入栈倒到输出栈内,否则不操作(因为输出栈有数字,不用操作,直接return即可)
if(b.isEmpty()){
while(!a.isEmpty()){
b.push(a.pop());
}
}
return b.pop();
}
/** Get the front element. */
public int peek() {
//如果输出栈为空,则把输入栈倒到输出栈内,否则不操作(因为输出栈有数字,不用操作,直接return即可)
if(b.isEmpty()){
while(!a.isEmpty()){
b.push(a.pop());
}
}
return b.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
//输出+输入都为空才可以哟
return a.isEmpty()&&b.isEmpty();
}
}
/**
* Your MyQueue object will be instantiated and called as such:
* MyQueue obj = new MyQueue();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.peek();
* boolean param_4 = obj.empty();
*/
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cs