lintcode-medium-Two Sum

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 returned answers (both index1 and index2) are NOT zero-based.

 

Notice

You may assume that each input would have exactly one solution

Example

numbers=[2, 7, 11, 15], target=9

return [1, 2]

Challenge

Either of the following solutions are acceptable:

• O(n) Space, O(nlogn) Time
• O(n) Space, O(n) Time

 

public class Solution {
    /*
     * @param numbers : An array of Integer
     * @param target : target = numbers[index1] + numbers[index2]
     * @return : [index1 + 1, index2 + 1] (index1 < index2)
     */
    public int[] twoSum(int[] numbers, int target) {
        // write your code here
        
        int[] res = new int[2];
        
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        
        for(int i = 0; i < numbers.length; i++){
            if(!map.containsKey(numbers[i])){
                map.put(target - numbers[i], i);
            }
            else{
                int in1 = map.get(numbers[i]) + 1;
                int in2 = i + 1;
                res[0] = in1;
                res[1] = in2;
                
                return res;
            }
        }
        
        return res;
    }
}