java求最短路径问题源程序_Java 所有节点对之间的最短路径

朱雀 2022-11-06 12:54 76阅读 0赞

import java.util.Arrays;

//Runtime: O(V^3). Shortest path between all the pairs of nodes, works with negative cycle.

public class FloydWarshall \{

/\*\*

来自 nowjava.com - 时 代 Java\*\*/

//gWeights\[i\]\[j\] must contain the weight of the edge ij if there is an edge i->j, 0 if i=j, otherwise +infinity if there is no edge i->j

/\*\*

\* @param gWeights it's a matrix V\*V where V is the number of verticies. gWeights\[u\]\[v\] = w if there is an edge between u and v of weight w, gWeights\[u\]\[u\]=0, gWeights\[u\]\[v\]=DOUBLE.POSITIVE\_INFINITY if there is no edge between u and v

\* @return matrix\[V\]\[V\] where matrix\[u\]\[v\]=min distance to go from u to v

\*/

public static double\[\]\[\] floydWarshall(double\[\]\[\] gWeights) \{

double\[\]\[\] minDistances = gWeights.clone();

int\[\]\[\] paths = new int\[gWeights.length\]\[gWeights\[0\].length\]; //paths\[i\]\[j\] contains the optimal predecessor of j to reach i

//initialize the current predessors with the edges of the graph

for (int i = 0; i < gWeights.length; i++) \{

for (int j = 0; j < gWeights\[0\].length; j++) \{

if (gWeights\[i\]\[j\] < Double.POSITIVE\_INFINITY && i != j) \{ //means there is an edge between i and j

paths\[i\]\[j\] = i; //mark i as the predecessor of j to reach i

\} else \{

paths\[i\]\[j\] = -1; //there is not edge, so mark -1

\}/\*\*来 自 nowjava - 时 代 Java\*\*/

//for every pair test if there is a shorter path gowing through another node

for (int k = 0; k < gWeights.length; k++) \{// test if ik->kj shorter than current i->j

for (int i = 0; i < gWeights.length; i++) \{

for (int j = 0; j < gWeights.length; j++) \{ //pair i,j

if (minDistances\[i\]\[j\] > minDistances\[i\]\[k\]

\+ minDistances\[k\]\[j\]) \{

minDistances\[i\]\[j\] = minDistances\[i\]\[k\]

\+ minDistances\[k\]\[j\];

paths\[i\]\[j\] = paths\[k\]\[j\]; //the predecessor of j to reach i is the predecessor of j to reach k

//if one distance from a node to itself changed to a negative value, it means that there is a negative cycle in the graph, => return null

for (int i = 0; i < minDistances.length; i++) \{

if (minDistances\[i\]\[i\] != 0) \{

return null; //there is a negative cycle in the graph

return minDistances;

public static void main(String\[\] args) \{

double\[\]\[\] gWeights = new double\[\]\[\] \{

\{ 0, 3, 6, 15 \},

\{ Double.POSITIVE\_INFINITY, 0, -2, Double.POSITIVE\_INFINITY \},

\{ Double.POSITIVE\_INFINITY, Double.POSITIVE\_INFINITY, 0, 2 \},

\{ 1, Double.POSITIVE\_INFINITY, Double.POSITIVE\_INFINITY, 0 \} \};

System.out.println("The weights matrix representing the graph :");

/\*\*代码未完, 请加载全部代码(NowJava.com).\*\*/

java求最短路径问题源程序_Java 所有节点对之间的最短路径

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