add 136

Author: andavid

README.md

@@ -20,7 +20,7 @@
 | 122  | [Best Time to Buy and Sell Stock II][122]   |
 | 189  | [Rotate Array][189]                         |
 | 217  | [Contains Duplicate][217]                   |
-
+| 136  | [Single Number][136]                        |
 
 [leetcode]: https://leetcode.com/problemset/all/
 [blankj]: https://github.com/Blankj/awesome-java-leetcode
@@ -31,3 +31,4 @@
 [122]: https://github.com/andavid/leetcode-java/blob/master/note/122/README.md
 [189]: https://github.com/andavid/leetcode-java/blob/master/note/189/README.md
 [217]: https://github.com/andavid/leetcode-java/blob/master/note/217/README.md
+[136]: https://github.com/andavid/leetcode-java/blob/master/note/136/README.md

note/136/README.md

@@ -0,0 +1,32 @@
+# [Single Number][title]
+
+## Description
+
+Given an array of integers, every element appears twice except for one. Find that single one.
+
+Note:
+Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
+
+## 思路
+
+给定一个数组，数组中除了一个数只出现了一次，其他数都出现了两次，找出那个数。
+
+把所有的数字进行异或运算即可。
+
+
+## [完整代码][src]
+
+```java
+class Solution {
+  public int singleNumber(int[] nums) {
+    int n = 0;
+    for (int num : nums) {
+      n ^= num;
+    }
+    return n;
+  }
+}
+```
+
+[title]: https://leetcode.com/problems/single-number
+[src]: https://github.com/andavid/leetcode-java/blob/master/src/com/andavid/leetcode/_136/Solution.java

src/com/andavid/leetcode/_136/Solution.java

@@ -0,0 +1,14 @@
+class Solution {
+  public int singleNumber(int[] nums) {
+    int n = 0;
+    for (int num : nums) {
+      n ^= num;
+    }
+    return n;
+  }
+
+  public static void main(String[] args) {
+    Solution solution = new Solution();
+    System.out.println(solution.singleNumber(new int[]{1, 2, 1}));
+  }
+}