下面Floyd算法中，横线处应该填入的是（    ）。

#include <iostream>

using namespace std;

#define N 21

#define INF 99999999

int map[N][N];

int main() {

int n, m, t1, t2, t3;

cin >> n >> m;

for (int i = 1; i <= n; i++) {

for (int j = 1; j <= n; j++) {

if (i == j)

map[i][j] = 0; else

map[i][j] = INF;

}

}

for (int i = 1; i <= m; i++) {

cin >> t1 >> t2 >> t3;

map[t1][t2] = t3;

}

for (int k = 1; k <= n; k++)

     for (int i = 1; i <= n; i++)

          for (int j = 1; j <= n; j++)

               if (__________) // 在此处填入选项

                      map[i][j] = map[i][k] + map[k][j];

for (int i = 1; i <= n; i++) {

for (int j = 1; j <= n; j++) {

cout.width(4);

cout << map[i][j];

}

cout << endl;

}

}