Destination City

<-E 1436> Destination City

class Solution {
public:
    string destCity(vector<vector<string>>& paths) {
        unordered_map<string, int> map;
        for(int i = 0; i < paths.size(); i++){
            map[paths[i][0]]++;
        }
        
        for(int i = 0; i < paths.size(); i++){
            if(map[paths[i][1]] == 0) 
                return paths[i][1];
        }  
        
        return NULL;
    }
};