167. Two Sum II

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

解题思路：

unorder_map应用散列，注意一下count为0表示不存在这个数，为1为存在。

注意一下考虑到有重复数字所以我们先判断是否相加为target再放入散列。

class Solution {
public:
    vector<int> twoSum(vector<int>& numbers, int target) {

        unordered_map<int,int> store;
        vector<int> ret;
        for(int i=0;i<numbers.size();i++){


            if(store.count(target-numbers[i])>0){
                if(i>=store[target-numbers[i]]){
                    ret.push_back(store[target-numbers[i]]+1);
                    ret.push_back(i+1);
                }
                else {
                    ret.push_back(i+1);
                    ret.push_back(store[target-numbers[i]]+1);
                }

            }
            else  store[numbers[i]] = i;

        }
        return ret;
    }
};