【Leetcode】167. Two Sum II - Input array is sorted

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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

思路解析：
定义两个指针，一个从数组头开始遍历，一个从数组尾开始遍历，两者之和与target比较，如果和小于target,那么头指针加1，如果和大于target，那么尾指针减1.

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