1.TwoSum

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, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,Because nums[0] + nums[1] = 2 + 7 = 9,return [0, 1].

public class Solution2 {
public int[] twoSum(int[] nums, int target) {
   Map<Integer, Integer> map = new HashMap<Integer, Integer>();
   int[] ret = new int[2];
   for (int i = 0; i< nums.length; i++) {
       if (map.containsKey(target-nums[i])) {
           ret[0] = map.get(target-nums[i]);
           ret[1] = i;
           break;
       }
       map.put(nums[i], i);
   }
   return ret;
}
}