[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.

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

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思路：数组为有序的，所以可以用双向索引，i=0,j=numbers.size()-1 ,当numbers[i]+numbers[j]>target时，j--，当小于时i++，直到找到为止。代码如下：

#include<iostream>#include<vector>using namespace std;vector<int> twoSum(vector<int>& numbers, int target) {        vector<int> res;        int i=0,j=numbers.size()-1;while(i!=j) {if((numbers[i]+numbers[j])==target){res.push_back(i+1);res.push_back(j+1);break;}if((numbers[i]+numbers[j])>target)j--;else i++;}return  res;    }int main(){vector<int> numbers;numbers.push_back(1);numbers.push_back(2);numbers.push_back(3);numbers=twoSum(numbers,4);for(int i=0;i<numbers.size();i++)cout<<numbers[i]<<'\0';}