[167]Two Sum II - Input array is sorted

【题目描述】

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

【解题思路】

二分搜索，时间复杂度为O(n)，空间复杂度为O(1)

【代码】

class Solution {public:    vector<int> twoSum(vector<int>& numbers, int target) {        vector<int> vec;        int sz=numbers.size();        if(sz==0||sz==1) return vec;        int i=0,j=sz-1;        while(i<j){            int res=numbers[i]+numbers[j];            if(res==target){                vec.push_back(i+1);                vec.push_back(j+1);                break;            }            else if(res<target){                i++;            }            else j--;        }        return vec;    }};