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Update FloydWarshallSolver.java
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‎com/williamfiset/algorithms/graphtheory/FloydWarshallSolver.java

Lines changed: 90 additions & 92 deletions
Original file line numberDiff line numberDiff line change
@@ -20,98 +20,6 @@
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public class FloydWarshallSolver {
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/* Example usage. */
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// Creates a graph with n nodes. The adjacency matrix is constructed
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// such that the value of going from a node to itself is 0.
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public static double[][] createGraph(int n) {
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double[][] matrix = new double[n][n];
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for (int i = 0; i < n; i++) {
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java.util.Arrays.fill(matrix[i], POSITIVE_INFINITY);
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matrix[i][i] = 0;
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}
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return matrix;
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}
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public static void main(String[] args) {
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// Construct graph.
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int n = 7;
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double[][] m = createGraph(n);
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// Add some edge values.
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m[0][1] = 2;
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m[0][2] = 5;
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m[0][6] = 10;
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m[1][2] = 2;
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m[1][4] = 11;
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m[2][6] = 2;
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m[6][5] = 11;
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m[4][5] = 1;
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m[5][4] = -2;
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FloydWarshallSolver solver = new FloydWarshallSolver(m);
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double[][] dist = solver.getApspMatrix();
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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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System.out.printf("This shortest path from node %d to node %d is %.3f\n", i, j, dist[i][j]);
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// Prints:
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// This shortest path from node 0 to node 0 is 0.000
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// This shortest path from node 0 to node 1 is 2.000
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// This shortest path from node 0 to node 2 is 4.000
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// This shortest path from node 0 to node 3 is Infinity
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// This shortest path from node 0 to node 4 is -Infinity
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// This shortest path from node 0 to node 5 is -Infinity
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// This shortest path from node 0 to node 6 is 6.000
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// This shortest path from node 1 to node 0 is Infinity
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// This shortest path from node 1 to node 1 is 0.000
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// This shortest path from node 1 to node 2 is 2.000
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// This shortest path from node 1 to node 3 is Infinity
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// ...
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System.out.println();
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// Reconstructs the shortest paths from all nodes to every other nodes.
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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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List<Integer> path = solver.reconstructShortestPath(i, j);
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String str;
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if (path == null) {
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str = "HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)";
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} else if (path.size() == 0) {
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str = String.format("DOES NOT EXIST (node %d doesn't reach node %d)", i, j);
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} else {
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str = String.join(" -> ", path.stream()
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.map(Object::toString)
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.collect(java.util.stream.Collectors.toList()));
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str = "is: [" + str + "]";
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}
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System.out.printf("The shortest path from node %d to node %d %s\n", i, j, str);
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}
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}
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// Prints:
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// The shortest path from node 0 to node 0 is: [0]
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// The shortest path from node 0 to node 1 is: [0 -> 1]
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// The shortest path from node 0 to node 2 is: [0 -> 1 -> 2]
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// The shortest path from node 0 to node 3 DOES NOT EXIST (node 0 doesn't reach node 3)
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// The shortest path from node 0 to node 4 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 0 to node 5 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 0 to node 6 is: [0 -> 1 -> 2 -> 6]
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// The shortest path from node 1 to node 0 DOES NOT EXIST (node 1 doesn't reach node 0)
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// The shortest path from node 1 to node 1 is: [1]
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// The shortest path from node 1 to node 2 is: [1 -> 2]
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// The shortest path from node 1 to node 3 DOES NOT EXIST (node 1 doesn't reach node 3)
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// The shortest path from node 1 to node 4 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 1 to node 5 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 1 to node 6 is: [1 -> 2 -> 6]
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// The shortest path from node 2 to node 0 DOES NOT EXIST (node 2 doesn't reach node 0)
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// ...
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}
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private int n;
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private boolean solved;
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private double[][] dp;
@@ -204,6 +112,96 @@ public List<Integer> reconstructShortestPath(int start, int end) {
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return path;
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}
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/* Example usage. */
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// Creates a graph with n nodes. The adjacency matrix is constructed
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// such that the value of going from a node to itself is 0.
119+
public static double[][] createGraph(int n) {
120+
double[][] matrix = new double[n][n];
121+
for (int i = 0; i < n; i++) {
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java.util.Arrays.fill(matrix[i], POSITIVE_INFINITY);
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matrix[i][i] = 0;
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}
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return matrix;
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}
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public static void main(String[] args) {
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// Construct graph.
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int n = 7;
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double[][] m = createGraph(n);
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// Add some edge values.
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m[0][1] = 2;
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m[0][2] = 5;
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m[0][6] = 10;
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m[1][2] = 2;
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m[1][4] = 11;
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m[2][6] = 2;
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m[6][5] = 11;
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m[4][5] = 1;
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m[5][4] = -2;
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FloydWarshallSolver solver = new FloydWarshallSolver(m);
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double[][] dist = solver.getApspMatrix();
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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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System.out.printf("This shortest path from node %d to node %d is %.3f\n", i, j, dist[i][j]);
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// Prints:
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// This shortest path from node 0 to node 0 is 0.000
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// This shortest path from node 0 to node 1 is 2.000
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// This shortest path from node 0 to node 2 is 4.000
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// This shortest path from node 0 to node 3 is Infinity
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// This shortest path from node 0 to node 4 is -Infinity
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// This shortest path from node 0 to node 5 is -Infinity
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// This shortest path from node 0 to node 6 is 6.000
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// This shortest path from node 1 to node 0 is Infinity
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// This shortest path from node 1 to node 1 is 0.000
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// This shortest path from node 1 to node 2 is 2.000
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// This shortest path from node 1 to node 3 is Infinity
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// ...
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System.out.println();
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// Reconstructs the shortest paths from all nodes to every other nodes.
168+
for (int i = 0; i < n; i++) {
169+
for (int j = 0; j < n; j++) {
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List<Integer> path = solver.reconstructShortestPath(i, j);
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String str;
172+
if (path == null) {
173+
str = "HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)";
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} else if (path.size() == 0) {
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str = String.format("DOES NOT EXIST (node %d doesn't reach node %d)", i, j);
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} else {
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str = String.join(" -> ", path.stream()
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.map(Object::toString)
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.collect(java.util.stream.Collectors.toList()));
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str = "is: [" + str + "]";
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}
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System.out.printf("The shortest path from node %d to node %d %s\n", i, j, str);
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}
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}
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// Prints:
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// The shortest path from node 0 to node 0 is: [0]
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// The shortest path from node 0 to node 1 is: [0 -> 1]
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// The shortest path from node 0 to node 2 is: [0 -> 1 -> 2]
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// The shortest path from node 0 to node 3 DOES NOT EXIST (node 0 doesn't reach node 3)
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// The shortest path from node 0 to node 4 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 0 to node 5 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 0 to node 6 is: [0 -> 1 -> 2 -> 6]
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// The shortest path from node 1 to node 0 DOES NOT EXIST (node 1 doesn't reach node 0)
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// The shortest path from node 1 to node 1 is: [1]
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// The shortest path from node 1 to node 2 is: [1 -> 2]
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// The shortest path from node 1 to node 3 DOES NOT EXIST (node 1 doesn't reach node 3)
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// The shortest path from node 1 to node 4 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 1 to node 5 HAS AN ∞ NUMBER OF SOLUTIONS! (negative cycle case)
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// The shortest path from node 1 to node 6 is: [1 -> 2 -> 6]
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// The shortest path from node 2 to node 0 DOES NOT EXIST (node 2 doesn't reach node 0)
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// ...
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}
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}
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