60 lines
1.6 KiB
Java
60 lines
1.6 KiB
Java
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import java.util.Arrays;
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public class FloydWarshall {
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static final int INF = Integer.MAX_VALUE / 2;
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// precondition: d[i][i] == 0
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public static int[][] floydWarshall(int[][] d) {
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int n = d.length;
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int[][] pred = new int[n][n];
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for (int i = 0; i < n; i++)
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for (int j = 0; j < n; j++)
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pred[i][j] = (i == j || d[i][j] == INF) ? -1 : i;
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for (int k = 0; k < n; k++) {
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for (int i = 0; i < n; i++) {
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// if (d[i][k] == INF) continue;
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for (int j = 0; j < n; j++) {
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// if (d[k][j] == INF) continue;
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if (d[i][j] > d[i][k] + d[k][j]) {
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d[i][j] = d[i][k] + d[k][j];
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// d[i][j] = Math.max(d[i][j], -INF);
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pred[i][j] = pred[k][j];
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}
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}
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}
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}
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for (int i = 0; i < n; i++)
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if (d[i][i] < 0)
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return null;
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return pred;
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}
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public static int[] restorePath(int[][] pred, int i, int j) {
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int n = pred.length;
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int[] path = new int[n];
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int pos = n;
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while (true) {
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path[--pos] = j;
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if (i == j) break;
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j = pred[i][j];
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}
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return Arrays.copyOfRange(path, pos, n);
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}
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// Usage example
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public static void main(String[] args) {
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int[][] dist = {{0, 3, 2}, {0, 0, 1}, {INF, 0, 0}};
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int[][] pred = floydWarshall(dist);
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int[] path = restorePath(pred, 0, 1);
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System.out.println(0 == dist[0][0]);
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System.out.println(2 == dist[0][1]);
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System.out.println(2 == dist[0][2]);
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System.out.println(-1 == pred[0][0]);
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System.out.println(2 == pred[0][1]);
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System.out.println(0 == pred[0][2]);
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System.out.println(Arrays.equals(new int[]{0, 2, 1}, path));
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}
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}
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