LeetCode-167-Two Sum II - Input array is sorted-E

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本文介绍了一种在已排序的整数数组中寻找两个数使其和等于特定目标值的有效算法。利用双指针技巧从两端逼近，实现O(n)时间复杂度下的查找。输入数组为[2, 7, 11, 15]，目标值为9时，返回索引1和2。

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

本题可以用leetcode第一题的方法，由于nums数组是sorted的，所以还可以用下面的方法：

vector<int> twoSum(vector<int>& nums, int target) {
        int left=0,right=nums.size()-1;       
        while(left<right){
            if(nums[left]+nums[right]==target){
                vector<int>result{left+1,right+1};
                return result;
            }
            else if(nums[left]+nums[right]<target){
                left++;
            }
            else
                right--;        
        }
    }