leetcode167. Two Sum II - Input array is sorted

網址url：https://leetcode.com/problems/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.

Note: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.

Example:Input: numbers = [2,7,11,15], target = 9 Output: [1,2] Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.

解題思路：

雙指針

代碼：

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target) {
        vector<int> ret;
        int n = numbers.size();
        int l = 0;
        int r = n-1;
        while(l<r-1){
            int sum = numbers[l] + numbers[r];
            if(sum ==target){
                ret.push_back(l+1);
                ret.push_back(r+1);
                return ret;
            }
            if(sum <target){
                l++;
            }
            if(sum > target){
                r--;
            }
        }
        if(numbers[l] + numbers[r] == target){
            ret.push_back(l+1);
            ret.push_back(r+1);
            return ret;
        }
        return ret;
        
    }
};