[leetcode]167. Two Sum II - Input array is sorted

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 and you may not use the same element twice.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

解题思路

本题是two sum的变种题，其实比two sum还简单一些，因为已经排好序了，直接采用头尾下标的方法。

vector twoSum(vector& numbers, int target) {
        vector res;
        int number = numbers.size();
        
        int l = 0, r = number -1;
        while(l < r)
        {
            if(numbers[l] > target) break;
            if(numbers[l] + numbers[r] == target)
            {
                res.push_back(l+1);
                res.push_back(r+1);
                return res;
            }
            else if(numbers[l] + numbers[r] < target)
                l++;
            else{
                r--;
            }
        }
        return res;
    }