diff --git a/problems/0225.用队列实现栈.md b/problems/0225.用队列实现栈.md index 3457c4b3..3c134870 100644 --- a/problems/0225.用队列实现栈.md +++ b/problems/0225.用队列实现栈.md @@ -815,6 +815,89 @@ class MyStack { } } ``` +Scala: +使用两个队列模拟栈: +```scala +import scala.collection.mutable + +class MyStack() { + + val queue1 = new mutable.Queue[Int]() + val queue2 = new mutable.Queue[Int]() + + def push(x: Int) { + queue1.enqueue(x) + } + + def pop(): Int = { + var size = queue1.size + // 将queue1中的每个元素都移动到queue2 + for (i <- 0 until size - 1) { + queue2.enqueue(queue1.dequeue()) + } + var res = queue1.dequeue() + // 再将queue2中的每个元素都移动到queue1 + while (!queue2.isEmpty) { + queue1.enqueue(queue2.dequeue()) + } + res + } + + def top(): Int = { + var size = queue1.size + for (i <- 0 until size - 1) { + queue2.enqueue(queue1.dequeue()) + } + var res = queue1.dequeue() + while (!queue2.isEmpty) { + queue1.enqueue(queue2.dequeue()) + } + // 最终还需要把res送进queue1 + queue1.enqueue(res) + res + } + + def empty(): Boolean = { + queue1.isEmpty + } +} +``` +使用一个队列模拟: +```scala +import scala.collection.mutable + +class MyStack() { + + val queue = new mutable.Queue[Int]() + + def push(x: Int) { + queue.enqueue(x) + } + + def pop(): Int = { + var size = queue.size + for (i <- 0 until size - 1) { + queue.enqueue(queue.head) // 把头添到队列最后 + queue.dequeue() // 再出队 + } + queue.dequeue() + } + + def top(): Int = { + var size = queue.size + var res = 0 + for (i <- 0 until size) { + queue.enqueue(queue.head) // 把头添到队列最后 + res = queue.dequeue() // 再出队 + } + res + } + + def empty(): Boolean = { + queue.isEmpty + } +} +``` -----------------------