Two Sum

Given an array of integers, 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

函式返回這兩個數的索引，index1 必須小於 index2。注意，返回的索引不是從 0 開始的。

假設對於每個輸入只有一個解。

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

分析：

    使用 map，鍵為陣列值，值為陣列索引

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        if(nums.empty())//空
        {
            return vector<int>();
        }
        
        map<int, int> addend;
        int numsSize = nums.size();
        for(int index = 0; index < numsSize; ++index)
        {
            if(addend.find(target - nums[index]) == addend.end())//另一個加數不在 map 中，加入 map
            {
                addend[nums[index]] = index + 1;
            }
            else //找到兩個合法的數
            {
                vector<int> ret;
                ret.push_back(addend[target - nums[index]]);
                ret.push_back(index + 1);
                
                return ret;
            }
        }
        
        return vector<int>();
    }
};