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package class16;
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import java.util.Comparator;
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import java.util.HashSet;
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import java.util.PriorityQueue;
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import java.util.Set;
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// undirected graph only
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public class Code05_Prim {
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public static class EdgeComparator implements Comparator<Edge> {
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@Override
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public int compare(Edge o1, Edge o2) {
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return o1.weight - o2.weight;
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}
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}
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public static Set<Edge> primMST(Graph graph) {
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// 解锁的边进入小根堆
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PriorityQueue<Edge> priorityQueue = new PriorityQueue<>(new EdgeComparator());
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// 哪些点被解锁出来了
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HashSet<Node> nodeSet = new HashSet<>();
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Set<Edge> result = new HashSet<>(); // 依次挑选的的边在result里
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for (Node node : graph.nodes.values()) { // 随便挑了一个点
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// node 是开始点
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if (!nodeSet.contains(node)) {
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nodeSet.add(node);
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for (Edge edge : node.edges) { // 由一个点，解锁所有相连的边
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priorityQueue.add(edge);
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}
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while (!priorityQueue.isEmpty()) {
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Edge edge = priorityQueue.poll(); // 弹出解锁的边中，最小的边
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Node toNode = edge.to; // 可能的一个新的点
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if (!nodeSet.contains(toNode)) { // 不含有的时候，就是新的点
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nodeSet.add(toNode);
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result.add(edge);
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for (Edge nextEdge : toNode.edges) {
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priorityQueue.add(nextEdge);
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}
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}
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}
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}
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// break;
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}
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return result;
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}
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// 请保证graph是连通图
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// graph[i][j]表示点i到点j的距离，如果是系统最大值代表无路
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// 返回值是最小连通图的路径之和
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public static int prim(int[][] graph) {
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int size = graph.length;
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int[] distances = new int[size];
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boolean[] visit = new boolean[size];
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visit[0] = true;
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for (int i = 0; i < size; i++) {
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distances[i] = graph[0][i];
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}
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int sum = 0;
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for (int i = 1; i < size; i++) {
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int minPath = Integer.MAX_VALUE;
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int minIndex = -1;
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for (int j = 0; j < size; j++) {
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if (!visit[j] && distances[j] < minPath) {
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minPath = distances[j];
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minIndex = j;
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}
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}
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if (minIndex == -1) {
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return sum;
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}
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visit[minIndex] = true;
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sum += minPath;
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for (int j = 0; j < size; j++) {
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if (!visit[j] && distances[j] > graph[minIndex][j]) {
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distances[j] = graph[minIndex][j];
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}
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}
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}
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return sum;
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}
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public static void main(String[] args) {
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System.out.println("hello world!");
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}
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}
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