You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
60 lines
1.6 KiB
Java
60 lines
1.6 KiB
Java
import java.util.Arrays;
|
|
|
|
public class FloydWarshall {
|
|
|
|
static final int INF = Integer.MAX_VALUE / 2;
|
|
|
|
// precondition: d[i][i] == 0
|
|
public static int[][] floydWarshall(int[][] d) {
|
|
int n = d.length;
|
|
int[][] pred = new int[n][n];
|
|
for (int i = 0; i < n; i++)
|
|
for (int j = 0; j < n; j++)
|
|
pred[i][j] = (i == j || d[i][j] == INF) ? -1 : i;
|
|
for (int k = 0; k < n; k++) {
|
|
for (int i = 0; i < n; i++) {
|
|
// if (d[i][k] == INF) continue;
|
|
for (int j = 0; j < n; j++) {
|
|
// if (d[k][j] == INF) continue;
|
|
if (d[i][j] > d[i][k] + d[k][j]) {
|
|
d[i][j] = d[i][k] + d[k][j];
|
|
// d[i][j] = Math.max(d[i][j], -INF);
|
|
pred[i][j] = pred[k][j];
|
|
}
|
|
}
|
|
}
|
|
}
|
|
for (int i = 0; i < n; i++)
|
|
if (d[i][i] < 0)
|
|
return null;
|
|
return pred;
|
|
}
|
|
|
|
public static int[] restorePath(int[][] pred, int i, int j) {
|
|
int n = pred.length;
|
|
int[] path = new int[n];
|
|
int pos = n;
|
|
while (true) {
|
|
path[--pos] = j;
|
|
if (i == j) break;
|
|
j = pred[i][j];
|
|
}
|
|
return Arrays.copyOfRange(path, pos, n);
|
|
}
|
|
|
|
// Usage example
|
|
public static void main(String[] args) {
|
|
int[][] dist = {{0, 3, 2}, {0, 0, 1}, {INF, 0, 0}};
|
|
int[][] pred = floydWarshall(dist);
|
|
int[] path = restorePath(pred, 0, 1);
|
|
|
|
System.out.println(0 == dist[0][0]);
|
|
System.out.println(2 == dist[0][1]);
|
|
System.out.println(2 == dist[0][2]);
|
|
System.out.println(-1 == pred[0][0]);
|
|
System.out.println(2 == pred[0][1]);
|
|
System.out.println(0 == pred[0][2]);
|
|
System.out.println(Arrays.equals(new int[]{0, 2, 1}, path));
|
|
}
|
|
}
|