1. Two Sum

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].

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.
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public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        if(numbers.length <= 1){
            return new int[]{};
        }
        int ans[] = new int[2];
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for(int idx = 0; idx < numbers.length; idx++){
            map.put(numbers[idx], idx);
        }
        for(int idx = 0; idx < numbers.length; idx++){
            if(map.containsKey(target - numbers[idx]) && map.get(target - numbers[idx]) != idx ){
                 ans[0] = Math.min(map.get(target - numbers[idx]), idx);
                 ans[1] = Math.max(map.get(target - numbers[idx]), idx);
                 break;
            }
        }
        return ans;
        
    }
}