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 (map[i][j] > map[i][k] + map[k][j]) ________; // 在此处填入选项 for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { cout.width(4); cout << map[i][j]; } cout << endl; } }