@@ -815,6 +815,89 @@ class MyStack {
815815 }
816816}
817817```
818+ Scala:
818819
820+ 使用两个队列模拟栈:
821+ ``` scala
822+ import scala .collection .mutable
823+ 824+ class MyStack () {
825+ 826+ val queue1 = new mutable.Queue [Int ]()
827+ val queue2 = new mutable.Queue [Int ]()
828+ 829+ def push (x : Int ) {
830+ queue1.enqueue(x)
831+ }
832+ 833+ def pop (): Int = {
834+ var size = queue1.size
835+ // 将queue1中的每个元素都移动到queue2
836+ for (i <- 0 until size - 1 ) {
837+ queue2.enqueue(queue1.dequeue())
838+ }
839+ var res = queue1.dequeue()
840+ // 再将queue2中的每个元素都移动到queue1
841+ while (! queue2.isEmpty) {
842+ queue1.enqueue(queue2.dequeue())
843+ }
844+ res
845+ }
846+ 847+ def top (): Int = {
848+ var size = queue1.size
849+ for (i <- 0 until size - 1 ) {
850+ queue2.enqueue(queue1.dequeue())
851+ }
852+ var res = queue1.dequeue()
853+ while (! queue2.isEmpty) {
854+ queue1.enqueue(queue2.dequeue())
855+ }
856+ // 最终还需要把res送进queue1
857+ queue1.enqueue(res)
858+ res
859+ }
860+ 861+ def empty (): Boolean = {
862+ queue1.isEmpty
863+ }
864+ }
865+ ```
866+ 使用一个队列模拟:
867+ ``` scala
868+ import scala .collection .mutable
869+ 870+ class MyStack () {
871+ 872+ val queue = new mutable.Queue [Int ]()
873+ 874+ def push (x : Int ) {
875+ queue.enqueue(x)
876+ }
877+ 878+ def pop (): Int = {
879+ var size = queue.size
880+ for (i <- 0 until size - 1 ) {
881+ queue.enqueue(queue.head) // 把头添到队列最后
882+ queue.dequeue() // 再出队
883+ }
884+ queue.dequeue()
885+ }
886+ 887+ def top (): Int = {
888+ var size = queue.size
889+ var res = 0
890+ for (i <- 0 until size) {
891+ queue.enqueue(queue.head) // 把头添到队列最后
892+ res = queue.dequeue() // 再出队
893+ }
894+ res
895+ }
896+ 897+ def empty (): Boolean = {
898+ queue.isEmpty
899+ }
900+ }
901+ ```
819902-----------------------
820903<div align =" center " ><img src =https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width =500 > </img ></div >
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