algorithms/cpp/twoSum/twoSum.II.cpp

// Source : https://oj.leetcode.com/problems/two-sum-ii-input-array-is-sorted/
// Author : Hao Chen
// Date   : 2014-12-25

/********************************************************************************** 
* 
* Given an array of integers that is already sorted in ascending order, 
* 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.
* 
* You may assume that each input would have exactly one solution.
* 
* Input: numbers={2, 7, 11, 15}, target=9
* Output: index1=1, index2=2 
* 
**********************************************************************************/


class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        vector<int> result;
        int low=0, high = numbers.size()-1;
        while (low < high){
            if (numbers[low] + numbers[high] == target){
                result.push_back(low+1);
                result.push_back(high+1);
                return result;
            }else{
                numbers[low] + numbers[high] > target ? high-- : low++;
            }
        }
        
        return result;
    }
};