Add solution 344

Author: yanglbme

README.md

@@ -22,6 +22,7 @@ Complete solutions to Leetcode problems, updated daily.
 | 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` |
+| 344 | [Reverse String](https://github.com/yanglbme/leetcode/tree/master/solution/344.Reverse%20String) | `Two Pointers`, `String` |
 | 876 | [Middle of the Linked List](https://github.com/yanglbme/leetcode/tree/master/solution/876.Middle%20of%20the%20Linked%20List) | `Linked List` |
 
 

solution/344.Reverse String/README.md

@@ -0,0 +1,41 @@
+## 反转字符串
+### 题目描述
+
+编写一个函数，其作用是将输入的字符串反转过来。
+
+示例 1:
+```
+输入: "hello"
+输出: "olleh"
+```
+
+示例 2:
+```
+输入: "A man, a plan, a canal: Panama"
+输出: "amanaP :lanac a ,nalp a ,nam A"
+```
+
+### 解法
+本题利用双指针解决。
+
+```java
+class Solution {
+    public String reverseString(String s) {
+        if (s == null || s.length() < 2) {
+            return s;
+        }
+        char[] chars = s.toCharArray();
+        int p = 0;
+        int q = chars.length - 1;
+        while (p < q) {
+            char tmp = chars[p];
+            chars[p] = chars[q];
+            chars[q] = tmp;
+            ++p;
+            --q;
+        }
+        return String.valueOf(chars);
+    }
+    
+}
+```

solution/344.Reverse String/Solution.java

@@ -0,0 +1,19 @@
+class Solution {
+    public String reverseString(String s) {
+        if (s == null || s.length() < 2) {
+            return s;
+        }
+        char[] chars = s.toCharArray();
+        int p = 0;
+        int q = chars.length - 1;
+        while (p < q) {
+            char tmp = chars[p];
+            chars[p] = chars[q];
+            chars[q] = tmp;
+            ++p;
+            --q;
+        }
+        return String.valueOf(chars);
+    }
+
+}