1. Two Sum

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

思路：利用哈希容器快速查找。

class Solution {
public:
vector<int> twoSum(vector<int> &numbers, int target){
unordered_map<int, int> hash;
vector<int> result;
for (int i = 0; i < numbers.size(); i++) {
int numberToFind = target - numbers[i];
if (hash.find(numberToFind) != hash.end()) {
result.push_back(hash[numberToFind]);
result.push_back(i);
return result;
}
hash[numbers[i]] = i;
}
return result;
}
};