[백준 1507] 궁금한 민호 (Floyd-Warshall) (C/C++) (★★)

#include <stdio.h>
#include <iostream>
#include <vector>
#include <map>
using namespace std;
 
int N;
int graph[25][25];
int road[25][25];
int roadCnt; 
int sum;
bool flag = false;
 
void floyd()
{
    for(int k = 1; k <= N; k++)
    {
        for(int i = 1; i <= N; i++)
        {
            for(int j = 1; j <= N; j++)
            {
                if(i == j || j == k || i == k)
                {
                    continue;
                }
                
                if(graph[i][k] + graph[k][j] == graph[i][j])
                {
                    // road[i][j] = 1 구간은 필요없음 
                    road[i][j] = 1;
                }
                else if(graph[i][k] + graph[k][j] < graph[i][j])
                {
                    flag = true;
                    return;
                }
            }    
        }
    } 
}
 
int main(void)
{
//    freopen("B1507_input.txt", "r", stdin);
    
    cin >> N;
    
    for(int i = 1; i <= N; i++)
    {
        for(int j = 1; j <= N; j++)
        {
            cin >> graph[i][j];
        }
    }
    
    floyd();
    
    if(flag)
    {
        cout << "-1";
    }
    else
    {
        for(int i = 1; i <= N; i++)
        {
            for(int j = i; j <= N; j++)
            {
                if(i == j)
                {
                    continue;
                }
                
                if(road[i][j] == 0)
                {
                    roadCnt++;
                    sum += graph[i][j];
                }
            }
        }
        
        cout << sum;
    }
    
    return 0;
}