Merge pull request #472 from TTWShell/bugfix/232

232: impl queue using stacks

Author: TTWShell

leetcode/stack/MyQueue.go

@@ -16,7 +16,8 @@ You may assume that all operations are valid (for example, no pop or peek operat
 package lstack
 
 type MyQueue struct {
-	q []int
+	stack1 []int
+	stack2 []int
 }
 
 /** Initialize your data structure here. */
@@ -25,24 +26,32 @@ func MyQueueConstructor() MyQueue {
 }
 
 /** Push element x to the back of queue. */
-func (this *MyQueue) Push(x int) {
-	// 可以考虑两个 []int 提高push性能，代价是pop／peek 性能降低
-	this.q = append([]int{x}, this.q...)
+func (m *MyQueue) Push(x int) {
+	m.stack1 = append(m.stack1, x)
 }
 
 /** Removes the element from in front of queue and returns that element. */
-func (this *MyQueue) Pop() int {
-	r := this.q[len(this.q)-1]
-	this.q = this.q[:len(this.q)-1]
-	return r
+func (m *MyQueue) Pop() int {
+	m.Peek()
+	top := len(m.stack2) - 1
+	value := m.stack2[len(m.stack2)-1]
+	m.stack2 = m.stack2[:top]
+	return value
 }
 
 /** Get the front element. */
-func (this *MyQueue) Peek() int {
-	return this.q[len(this.q)-1]
+func (m *MyQueue) Peek() int {
+	if len(m.stack2) == 0 {
+		for len(m.stack1) > 0 {
+			top := len(m.stack1) - 1
+			m.stack2 = append(m.stack2, m.stack1[top])
+			m.stack1 = m.stack1[:top]
+		}
+	}
+	return m.stack2[len(m.stack2)-1]
 }
 
 /** Returns whether the queue is empty. */
-func (this *MyQueue) Empty() bool {
-	return len(this.q) == 0
+func (m *MyQueue) Empty() bool {
+	return len(m.stack1) == 0 && len(m.stack2) == 0
 }

leetcode/stack/MyQueue_test.go

@@ -1,25 +1,23 @@
 package lstack
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
 
 func Test_MyQueue(t *testing.T) {
+	assert := assert.New(t)
+
 	myqueue := MyQueueConstructor()
 	myqueue.Push(1)
 	myqueue.Push(2)
 	myqueue.Push(3)
 
-	if r := myqueue.Empty(); r != false {
-		t.Fatal("Empty:", r)
-	}
-
-	if r := myqueue.Peek(); r != 1 {
-		t.Fatal("Peek:", r)
-	}
-
-	myqueue.Pop()
-	myqueue.Pop()
-	myqueue.Pop()
-	if r := myqueue.Empty(); r != true {
-		t.Fatal("Empty:", r)
-	}
+	assert.False(myqueue.Empty())
+	assert.Equal(1, myqueue.Peek())
+	assert.Equal(1, myqueue.Pop())
+	assert.Equal(2, myqueue.Pop())
+	assert.Equal(3, myqueue.Pop())
+	assert.True(myqueue.Empty())
 }