189 improve

最快的答案是三次翻转

Author: aQua

Algorithms/0189.rotate-array/README.md

@@ -17,6 +17,10 @@ Could you do it in-place with O(1) extra space?
 Related problem: [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/)
 
 ## 解题思路
+###  三次翻转
+1. nums 整体翻转
+1. nums[:k] 翻转
+1. nums[k:] 翻转
 
-
+### 递归交换
 见程序注释

Algorithms/0189.rotate-array/rotate-array.go

@@ -1,11 +1,26 @@
 package Problem0189
 
 func rotate(nums []int, k int) {
-	for i := 0; i < k; i++ {
-		temp := nums[len(nums)-1]
-		for j := len(nums) - 1; j > 0; j-- {
-			nums[j] = nums[j-1]
-		}
-		nums[0] = temp
+	// 我已经假定 k >= 0
+
+	n := len(nums)
+
+	if k > n {
+		k %= n
+	}
+	if k == 0 || k == n {
+		return
+	}
+
+	reverse(nums, 0, n-1)
+	reverse(nums, 0, k-1)
+	reverse(nums, k, n-1)
+}
+
+func reverse(nums []int, i, j int) {
+	for i < j {
+		nums[i], nums[j] = nums[j], nums[i]
+		i++
+		j--
 	}
 }

Algorithms/0189.rotate-array/rotate-array_test.go

@@ -28,6 +28,24 @@ func Test_Problem0189(t *testing.T) {
 
 	qs := []question{
 
+		question{
+			para{
+				[]int{1, 2, 3, 4, 5, 6, 7}, 14,
+			},
+			ans{
+				[]int{1, 2, 3, 4, 5, 6, 7},
+			},
+		},
+
+		question{
+			para{
+				[]int{1, 2, 3, 4, 5, 6, 7}, 7,
+			},
+			ans{
+				[]int{1, 2, 3, 4, 5, 6, 7},
+			},
+		},
+
 		question{
 			para{
 				[]int{1, 2, 3, 4, 5, 6, 7}, 3,