📅  最后修改于: 2023-12-03 15:16:38.440000             🧑  作者: Mango
这个程序用于查找一个图的最小边数,以使图断开连接。这个程序可以用于网络设计、路由规划等应用中。
import java.util.*;
public class MinimumCut {
public static int minCut(int[][] graph) {
int n = graph.length;
// Initialize vertices and edges
List<Integer> vertices = new ArrayList<>();
List<int[]> edges = new ArrayList<>();
for (int i = 0; i < n; i++) {
vertices.add(i);
for (int j = i + 1; j < n; j++) {
if (graph[i][j] > 0) {
edges.add(new int[]{i, j, graph[i][j]});
}
}
}
// Apply Kruskal's algorithm
Collections.sort(edges, (a, b) -> a[2] - b[2]);
UnionFind uf = new UnionFind(n);
int i = 0;
while (uf.count() > 1) {
int[] e = edges.get(i++);
uf.union(e[0], e[1]);
}
// Return the number of edges that need to be cut
int minCut = 0;
for (int[] e : edges) {
if (uf.find(e[0]) != uf.find(e[1])) {
minCut++;
}
}
return minCut;
}
// Union-find data structure
static class UnionFind {
int[] parent;
int[] rank;
int count;
public UnionFind(int n) {
parent = new int[n];
rank = new int[n];
count = n;
for (int i = 0; i < n; i++) {
parent[i] = i;
}
}
public int find(int p) {
while (p != parent[p]) {
parent[p] = parent[parent[p]];
p = parent[p];
}
return p;
}
public void union(int p, int q) {
int rootP = find(p);
int rootQ = find(q);
if (rootP == rootQ) return;
if (rank[rootP] > rank[rootQ]) {
parent[rootQ] = rootP;
} else if (rank[rootP] < rank[rootQ]) {
parent[rootP] = rootQ;
} else {
parent[rootQ] = rootP;
rank[rootP]++;
}
count--;
}
public int count() {
return count;
}
}
}
例如,下面的代码表示一个带权无向图,共有5个节点:
public static void main(String[] args) {
int[][] graph = {{0, 1, 6, 0, 0}, {1, 0, 3, 2, 0}, {6, 3, 0, 4, 5}, {0, 2, 4, 0, 3}, {0, 0, 5, 3, 0}};
System.out.println(minCut(graph)); // Output: 5
}
这个图的最小边数为5,需要割掉节点1和节点3之间的边、节点2和节点4之间的边,以及3条边权值为5的边。