两数之和

LRH1993 · LRH1993 · commit 82e754974f3a · 2017-10-13T09:47:52.000+08:00
diff --git a/SUMMARY.md b/SUMMARY.md
@@ -197,6 +197,7 @@
     - [Subarray Sum](/algorithm/LeetCode/Array/Subarray-Sum.md)
     - [Plus One](/algorithm/LeetCode/Array/plus-one.md) 
     - [Palindrome Number](/algorithm/LeetCode/Array/Palindrome-Number.md)
+    - [Two Sum](/algorithm/LeetCode/Array/Two-Sum.md)
   - [String](/algorithm/LeetCode/String.md)
     - [Restore IP Addresses](/algorithm/LeetCode/String/ip.md)
 
diff --git a/algorithm/LeetCode/Array/Two-Sum.md b/algorithm/LeetCode/Array/Two-Sum.md
@@ -0,0 +1,46 @@
+## 一、题目
+
+>Given an array of integers, return indices of the two numbers such that they add up to a specific target.
+>
+>You may assume that each input would have exactly one solution.
+>
+>Example:
+>
+>Given nums = [2, 7, 11, 15], target = 9,
+>Because nums[0] + nums[1] = 2 + 7 = 9,
+>return [0, 1].
+
+给定一个整型数组，找出能相加起来等于一个特定目标数字的两个数。
+
+## 二、解题思路
+
+用hashmap，hashmap是内部存储方式为哈希表的map结构。遍历数组，其中key存放目标值减去当前值，value存放对应索引。如果在遍历过程中发现map中存在与当前值相等的key，则返回结果。
+
+## 三、解题代码
+
+```java
+public class Solution {
+    /*
+     * @param numbers : An array of Integer
+     * @param target : target = numbers[index1] + numbers[index2]
+     * @return : [index1 + 1, index2 + 1] (index1 < index2)
+         numbers=[2, 7, 11, 15],  target=9
+         return [1, 2]
+     */
+    public int[] twoSum(int[] numbers, int target) {
+        HashMap<Integer,Integer> map = new HashMap<>();
+
+        for (int i = 0; i < numbers.length; i++) {
+            if (map.get(numbers[i]) != null) {
+                int[] result = {map.get(numbers[i]) + 1, i + 1};
+                return result;
+            }
+            map.put(target - numbers[i], i);
+        }
+        
+        int[] result = {};
+        return result;
+    }
+}
+```
+
