Two Sum II - Input array is sorted

一、问题描述

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
二、思路

由于本题只有两个数，而且数组是有序的，所以根据二分查找的思路即可，如果找到等于target的两个数，直接返回下标；找不到直接返回空。

三、代码

class Solution {
public:
vector<int> twoSum(vector<int>& numbers, int target) {
int p1 = 0, p2 = numbers.size() - 1;
while(p1 < p2){
if(numbers[p1] + numbers[p2] > target) --p2;
else if(numbers[p1] + numbers[p2] < target) ++p1;
else return vector<int>({p1 + 1, p2 + 1});
}
return vector<int>();
}
};