[lintcode medium] Two sum

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.

 

Example

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

return [1, 2]

Note

You may assume that each input would have exactly one solution

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[] result=new int[2];
       
        if(numbers==null || numbers.length==0) return result;

        int n=numbers.length;
       
        for(int i=0;i<n;i++)
        {
            int left=n-1;
            while(left>i)
            {
              int sum=numbers[i]+numbers[left];
              if(sum==target)
              {
                 result[0]=i+1;
                 result[1]=left+1;
                 return result;
              }
              else
              {
                  left--;
              }
            }
        }
       
        return result;
    }
}