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p232

admin 11月 12, 2020 0

LeetCode p232 Implement Queue using Stacks 题解

1.题目：

Implement the following operations of a queue using stacks.

push(x) -- Push element x to the back of queue.
pop() -- Removes the element from in front of queue.
peek() -- Get the front element.
empty() -- Return whether the queue is empty.

题意：

用栈实现队列

2.解题思路:

见代码，两个栈。

3.代码

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class  {
    
	Stack<Integer> stack1 = new Stack<Integer>();
	Stack<Integer> stack2 = new Stack<Integer>();

	public void push(int x) {
		stack2.add(x);
	}

	// Removes the element from in front of queue.
	public void pop() {
		if (stack1.empty()) {
			while (!stack2.empty()){
				// 移除
				stack1.add(stack2.pop());
			}
			stack1.pop();
		} else {
			stack1.pop();
		}
	}

	// Get the front element.
	public int peek() {
		if (stack1.empty()) {
			while (!stack2.empty()){
				// 移除
				stack1.add(stack2.pop());
			}
			return stack1.peek();
		} else {
			return stack1.peek();
		}
	}

	// Return whether the queue is empty.
	public boolean empty() {
		return stack1.empty() && stack2.empty();
	}
}

4.一些总结：