LeetCode.225_[栈]_用队列实现栈

1.题目

2.解题思路

每次入队时，把之前队列中的数一个个出队再入队，操作结束后，最后入队的在队头（这里可以用一个队列来实现，而我用来一个数组来存储数据，可以优化）

3.代码实现

class MyStack {
    Queue<Integer> stack;
    /** Initialize your data structure here. */
    public MyStack() {
        stack = new LinkedList<>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
    	int size = stack.size();
    	int[] arr = new int[size]; 
    	for (int i = 0; i < size; i++) {
			arr[i] = stack.poll();
		}
    	stack.add(x);
    	for (int i = 0; i < size; i++) {
			stack.add(arr[i]);
		}
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return stack.poll();
    }
    
    /** Get the top element. */
    public int top() {
        return stack.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return stack.isEmpty();
    }
}