Two Sum

• brute force
  逐个找

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        for(int i = 0 ; i < nums.size()-1 ; i++)
        {
            for(int j = i+1; j < nums.size() ; j++)
            {
                int sum = nums[i] + nums[j];
                if(sum == target)
                {
                    result.push_back(i);
                    result.push_back(j);
                    return result;
                }
            }
        }
    }
};

• One-pass Hash Table
  这里用了map，所以看一下是否有这个complement的值就行，不用回去一个一个地翻

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        map<int,int> m;
        for(int i = 0 ; i < nums.size() ; i++ )
        {
            int complement = target - nums[i];
            if(m.find(complement)!=m.end())
            {
                result.push_back(i);
                result.push_back(m[complement]);
                return result;
            }
            else
                m.insert(pair<int,int>(nums[i],i));
        }      
    }
};