1_TwoSum.java

/*
 * Given an array of integers, find two numbers such that they add up to a 
 * specific target number.
 * The function twoSum should return indices of the two numbers such that they 
 * add up to the target, where index1 must be less than index2. Please note 
 * that your re * turned answers (both index1 and index2) are not zero-based.
 * You may assume that each input would have exactly one solution.
 * Input: numbers={2, 7, 11, 15}, target=9
 * Output: index1=1, index2=2
 * 
 */

public class Two_Sum {
    public int[] twoSum(int[] numbers, int target) {
        int[] res = new int[2];
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();//add parentheses
        for(int i=0; i<numbers.length; i++) {
            if(map.containsKey(numbers[i])) {
                int j = map.get(numbers[i]);
                res[0] = j;
                res[1] = i + 1;
                break;
            }
            map.put(target - numbers[i], i + 1);
        }
        
        return res;
    }
    
    public static void main(String[] args){
    	Two_Sum slt = new Two_Sum();
    	int[] numbers = {2, 9, 7, 17};
    	int target = 9;
    	int[] index = new int[2];
		index = slt.twoSum(numbers, target);

		System.out.println("index1=" + index[0] + ", index2=" + index[1]);
    }
}