Add solution 189

Author: yanglbme

README.md

@@ -1,8 +1,15 @@
-# LeetCode
+
 ![LeetCode-GitHub](http://p9ucdlghd.bkt.clouddn.com/leetcode-github.png)
 
+<center>
+
 [![PRs Welcome](https://img.shields.io/badge/PRs-Welcome-brightgreen.svg)](http://makeapullrequest.com)
 [![Language](https://img.shields.io/badge/Lang-Java%2FPython%2FJS%2FCPP%2FGo%2F...-blue.svg)](https://github.com/yanglbme/leetcode)
+
+</center>
+
+# <center>LeetCode Solutions</center>
+
 ## Introduction
 Complete solutions to Leetcode problems, updated daily.
 
@@ -19,6 +26,7 @@ Complete solutions to Leetcode problems, updated daily.
 | 053 | [Maximum Subarray](https://github.com/yanglbme/leetcode/tree/master/solution/053.Maximum%20Subarray) | `Array`, `Divide and Conquer`, `Dynamic Programming` |
 | 070 | [Climbing Stairs](https://github.com/yanglbme/leetcode/tree/master/solution/070.Climbing%20Stairs) | `Dynamic Programming` |
 | 083 | [Remove Duplicates from Sorted List](https://github.com/yanglbme/leetcode/tree/master/solution/083.Remove%20Duplicates%20from%20Sorted%20List) | `Linked List` |
+| 189 | [Rotate Array](https://github.com/yanglbme/leetcode/tree/master/solution/189.Rotate%20Array) | `Array` |
 | 198 | [House Robber](https://github.com/yanglbme/leetcode/tree/master/solution/198.House%20Robber) | `Dynamic Programming` |
 | 203 | [Remove Linked List Elements](https://github.com/yanglbme/leetcode/tree/master/solution/203.Remove%20Linked%20List%20Elements) | `Linked List` |
 | 237 | [Delete Node in a Linked List](https://github.com/yanglbme/leetcode/tree/master/solution/237.Delete%20Node%20in%20a%20Linked%20List) | `Linked List` |

solution/189.Rotate Array/README.md

@@ -0,0 +1,57 @@
+## 旋转数组
+### 题目描述
+
+给定一个数组，将数组中的元素向右移动 k 个位置，其中 k 是非负数。
+
+示例 1:
+```
+输入: [1,2,3,4,5,6,7] 和 k = 3
+输出: [5,6,7,1,2,3,4]
+解释:
+向右旋转 1 步: [7,1,2,3,4,5,6]
+向右旋转 2 步: [6,7,1,2,3,4,5]
+向右旋转 3 步: [5,6,7,1,2,3,4]
+```
+
+示例 2:
+```
+输入: [-1,-100,3,99] 和 k = 2
+输出: [3,99,-1,-100]
+解释: 
+向右旋转 1 步: [99,-1,-100,3]
+向右旋转 2 步: [3,99,-1,-100]
+```
+
+说明:
+
+- 尽可能想出更多的解决方案，至少有三种不同的方法可以解决这个问题。
+- 要求使用空间复杂度为 O(1) 的原地算法。   
+
+### 解法
+先对整个数组做翻转，之后分别对 [0, k - 1]、[k, n - 1] 的子数组进行翻转，即可得到结果。
+
+```java
+class Solution {
+    public void rotate(int[] nums, int k) {
+        int n = nums.length;
+        k %= n;
+        if (n < 2 || k == 0) {
+            return;
+        }
+        
+        rotate(nums, 0, n - 1);
+        rotate(nums, 0, k - 1);
+        rotate(nums, k, n - 1);
+    }
+    
+    private void rotate(int[] nums, int start, int end) {
+        while (start < end) {
+            int t = nums[start];
+            nums[start] = nums[end];
+            nums[end] = t;
+            ++start;
+            --end;
+        }
+    }
+}
+```

solution/189.Rotate Array/Solution.java

@@ -0,0 +1,23 @@
+class Solution {
+    public void rotate(int[] nums, int k) {
+        int n = nums.length;
+        k %= n;
+        if (n < 2 || k == 0) {
+            return;
+        }
+        
+        rotate(nums, 0, n - 1);
+        rotate(nums, 0, k - 1);
+        rotate(nums, k, n - 1);
+    }
+    
+    private void rotate(int[] nums, int start, int end) {
+        while (start < end) {
+            int t = nums[start];
+            nums[start] = nums[end];
+            nums[end] = t;
+            ++start;
+            --end;
+        }
+    }
+}