167. Two Sum II

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.

Note:

Your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution and you may not use the same element twice.
Example:

Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target) {
        for (int i = 0; i < numbers.size(); i++){
            if(target - numbers[i] < numbers[i]) break; //second data smaller than current data
            if(binarySearch(numbers, i+1, numbers.size()-1, target-numbers[i])){
                vector<int> ret;
                ret.push_back(i+1);
                ret.push_back(pos+1);
                return ret;
            }
            
        }
    }
    
    bool binarySearch(vector<int>& numbers, int start, int end, int target){
        if(start > end) return false;
        
        int mid = start + (end - start )/2;
        if(numbers[mid] > target) return binarySearch(numbers, start, mid-1, target);
        else if (numbers[mid] < target) return binarySearch(numbers, mid+1, end, target);
        else{
            pos = mid;
            return true;
        }
    }
    
private:
    int pos; //second data index
};