【LeetCode】Two Sum

TwoSum

Given an array of integers,find two numbers such that they add up to a specific target number.

The function two Sum 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

方法一：

//暴力求解
class Solution1
{
public: 
	vector<int> twoSum(vector<int> &num, int target)
	{
		vector<int> rs;

		for (int i = 0; i < num.size(); ++i)
		{
			for (int j = i + 1; j < num.size(); j++)
			{
				if (num[i] + num[j] == target)
				{
					rs.push_back(i + 1);
					rs.push_back(j + 1);
					return rs;
				}
			}
		}
		return rs;
	}
};

方法二：

//用一个哈希表，存储每个数对应的下标
class Solution2
{
public:
	vector<int> twoSum(vector<int> &num, int target)
	{
		vector<int> rs;
		unordered_map<int, int> m;

		int i;
		for (i = 0; i < num.size(); i++)
			m[num[i]] = i;
		
		for (i = 0; i < num.size(); i++)
		{
			int sub = target - num[i];
			if (m.find(sub) != m.end() && m[sub] > i)
			{
				rs.push_back(i + 1);
				rs.push_back(m[sub] + 1);
				break;
			}
		}

		return rs;
	}
};