{ "data": { "question": { "questionId": "232", "questionFrontendId": "232", "categoryTitle": "Algorithms", "boundTopicId": 1448, "title": "Implement Queue using Stacks", "titleSlug": "implement-queue-using-stacks", "content": "
Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push
, peek
, pop
, and empty
).
Implement the MyQueue
class:
void push(int x)
Pushes element x to the back of the queue.int pop()
Removes the element from the front of the queue and returns it.int peek()
Returns the element at the front of the queue.boolean empty()
Returns true
if the queue is empty, false
otherwise.Notes:
\n\npush to top
, peek/pop from top
, size
, and is empty
operations are valid.\n
Example 1:
\n\n\nInput\n["MyQueue", "push", "push", "peek", "pop", "empty"]\n[[], [1], [2], [], [], []]\nOutput\n[null, null, null, 1, 1, false]\n\nExplanation\nMyQueue myQueue = new MyQueue();\nmyQueue.push(1); // queue is: [1]\nmyQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)\nmyQueue.peek(); // return 1\nmyQueue.pop(); // return 1, queue is [2]\nmyQueue.empty(); // return false\n\n\n
\n
Constraints:
\n\n1 <= x <= 9
100
calls will be made to push
, pop
, peek
, and empty
.pop
and peek
are valid.\n
Follow-up: Can you implement the queue such that each operation is amortized O(1)
time complexity? In other words, performing n
operations will take overall O(n)
time even if one of those operations may take longer.
请你仅使用两个栈实现先入先出队列。队列应当支持一般队列支持的所有操作(push
、pop
、peek
、empty
):
实现 MyQueue
类:
void push(int x)
将元素 x 推到队列的末尾int pop()
从队列的开头移除并返回元素int peek()
返回队列开头的元素boolean empty()
如果队列为空,返回 true
;否则,返回 false
说明:
\n\npush to top
, peek/pop from top
, size
, 和 is empty
操作是合法的。\n\n
示例 1:
\n\n\n输入:\n[\"MyQueue\", \"push\", \"push\", \"peek\", \"pop\", \"empty\"]\n[[], [1], [2], [], [], []]\n输出:\n[null, null, null, 1, 1, false]\n\n解释:\nMyQueue myQueue = new MyQueue();\nmyQueue.push(1); // queue is: [1]\nmyQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)\nmyQueue.peek(); // return 1\nmyQueue.pop(); // return 1, queue is [2]\nmyQueue.empty(); // return false\n\n\n
\n\n
提示:
\n\n1 <= x <= 9
100
次 push
、pop
、peek
和 empty
pop
或者 peek
操作)\n\n
进阶:
\n\nO(1)
的队列?换句话说,执行 n
个操作的总时间复杂度为 O(n)
,即使其中一个操作可能花费较长时间。\\u7248\\u672c\\uff1a \\u7f16\\u8bd1\\u65f6\\uff0c\\u5c06\\u4f1a\\u91c7\\u7528 \\u4e3a\\u4e86\\u4f7f\\u7528\\u65b9\\u4fbf\\uff0c\\u5927\\u90e8\\u5206\\u6807\\u51c6\\u5e93\\u7684\\u5934\\u6587\\u4ef6\\u5df2\\u7ecf\\u88ab\\u81ea\\u52a8\\u5bfc\\u5165\\u3002<\\/p>\"],\"java\":[\"Java\",\" \\u7248\\u672c\\uff1a \\u4e3a\\u4e86\\u65b9\\u4fbf\\u8d77\\u89c1\\uff0c\\u5927\\u90e8\\u5206\\u6807\\u51c6\\u5e93\\u7684\\u5934\\u6587\\u4ef6\\u5df2\\u88ab\\u5bfc\\u5165\\u3002<\\/p>\\r\\n\\r\\n \\u5305\\u542b Pair \\u7c7b: https:\\/\\/docs.oracle.com\\/javase\\/8\\/javafx\\/api\\/javafx\\/util\\/Pair.html <\\/p>\"],\"python\":[\"Python\",\" \\u7248\\u672c\\uff1a \\u4e3a\\u4e86\\u65b9\\u4fbf\\u8d77\\u89c1\\uff0c\\u5927\\u90e8\\u5206\\u5e38\\u7528\\u5e93\\u5df2\\u7ecf\\u88ab\\u81ea\\u52a8 \\u5bfc\\u5165\\uff0c\\u5982\\uff1aarray<\\/a>, bisect<\\/a>, 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use-after-free<\\/code>\\u9519\\u8bef\\u3002<\\/p>\\r\\n\\r\\n
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Python 2.7.12<\\/code><\\/p>\\r\\n\\r\\n
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out-of-bounds<\\/code>\\u548c
use-after-free<\\/code>\\u9519\\u8bef\\u3002<\\/p>\\r\\n\\r\\n
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rust 1.58.1<\\/code><\\/p>\\r\\n\\r\\n
PHP 8.1<\\/code>.<\\/p>\\r\\n\\r\\n