POJ 1611 The Suspects

并查集， 这道题默认情况下是 0 号学生是感染者。所以查找是只要查找跟 0 号学生在同一根结点下就行了。

package poj;import java.util.Scanner;public class Poj1611_20120814_0 {private static int [] set = new int[30001];private static int [] rank = new int[30001];public static void main(String[] args) {// TODO Auto-generated method stubScanner in = new Scanner(System.in);int n, m, i,j, count, temp;while(true){n = in.nextInt();m = in.nextInt();makeSet(n);if((m|n)==0){break;}for(i = 0; i < m; ++i){count = in.nextInt();if(count==0){continue;}temp = in.nextInt();for(j = 1; j < count; ++j){union(temp, in.nextInt());}}System.out.println(count(n));}}private static int count(int n){int i,res = 0;for(i = 0; i < n; ++i){if(findx(i) == findx(0)){ //查找时查找与 0 号学生在同一根结点下，即为受感染者。++res;}}return res;}private static void makeSet(int n){for(int i = 0; i < n; ++i){set[i] = i;rank[i] = 0;}}private static void union(int x, int y){x = findx(x);y = findx(y);if(rank[x] == rank[y]){set[y] = x;++rank[x];}else{if(rank[x]>rank[y]){set[y] = x;}else{set[x] = y;}}}private static int findx(int x){if(x!=set[x]){set[x] = findx(set[x]);}return set[x];}}