第一篇，2sum

 1 public class Solution {
 2     public int[] twoSum(int[] nums, int target) {
 3       int[] result = {-1, -1};
 4       if (nums == null || nums.length < 2) {
 5         return result;
 6       }
 7       HashMap<Integer, Integer> map = new HashMap();
 8       for (int i = 0; i < nums.length; i++) {
 9         if (map.containsKey(target - nums[i])) {
10           result[0] = map.get(target - nums[i]) + 1;
11           result[1] = i + 1;
12           break;
13         }
14         map.put(nums[i], i);
15       }
16       return result;
17     }
18 }