Add solution 001

Author: yanglbme

.gitignore

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+# Compiled class file
+*.class
+
+# Log file
+*.log
+
+# BlueJ files
+*.ctxt
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*

README.md

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+# LeetCode
+![LeetCode-GitHub](http://p9ucdlghd.bkt.clouddn.com/leetcode-github.png)
+
+[![PRs Welcome](https://img.shields.io/badge/PRs-Welcome-brightgreen.svg)](http://makeapullrequest.com)
+[![Java Version](https://img.shields.io/badge/Lang-Java-red.svg)](https://github.com/yanglbme/qa)
+## Introduction
+Complete solutions to Leetcode problems, updated daily.
+
+## Solution List
+
+### Easy
+
+| # | Title | Tags |
+|---|---|---|
+| 001 | [Two Sum](https://github.com/yanglbme/leetcode/tree/master/solution/001.Two%20Sum) | `Array`, `Hash Table` |
+
+### Medium
+
+| # | Title | Tags |
+|---|---|---|
+
+### Hard
+
+| # | Title | Tags |
+|---|---|---|
+
+## Contributions
+I'm looking for long-term contributors/partners to this repo! Send me PRs if you're interested! See the following:
+- Fork this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it to your local device.
+- Submit a pull request with your changes!
+
+## Contributors
+
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+| <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center>[<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="100px;"/><br /><sub><b>yanglbme</b></sub>](https://github.com/yanglbme)<br />[💻](https://github.com/yanglbme/leetcode/commits?author=yanglbme "Code") </center> | 
+|---|---|---|---|---|---|---|
+
+<!-- ALL-CONTRIBUTORS-LIST:END -->

solution/001.Two Sum/README.md

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+## 两数之和
+### 题目描述
+
+给定一个整数数组和一个目标值，找出数组中和为目标值的两个数。
+
+你可以假设每个输入只对应一种答案，且同样的元素不能被重复利用。
+
+示例:
+```
+给定 nums = [2, 7, 11, 15], target = 9
+
+因为 nums[0] + nums[1] = 2 + 7 = 9
+所以返回 [0, 1]
+```
+
+### 解法
+利用 HashMap 记录数组元素值和对应的下标，对于一个数 nums[i]，判断 target - nums[i] 是否存在 HashMap 中，存在的话，返回两个下标组成的数组。注意，已存在的元素下标在前，当前元素下标在后。
+
+```java
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < nums.length; ++i) {
+            if (map.containsKey(target - nums[i])) {
+                return new int[] {map.get(target - nums[i]), i};
+            }
+            map.put(nums[i], i);
+        }
+        return null;
+    }
+}
+```

solution/001.Two Sum/Solution.java

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+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < nums.length; ++i) {
+            if (map.containsKey(target - nums[i])) {
+                return new int[] {map.get(target - nums[i]), i};
+            }
+            map.put(nums[i], i);
+        }
+        return null;
+    }
+}