【九度OJ】1024【并查集】【BST】【畅通工程系列2007】

package Test1;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;

public class Test37_1024 {
	/**
	 * by qr jobdu 1024 2014-8-19
	 * 
	 * @throws IOException
	 */
	public static void main(String[] args) throws IOException {
		StreamTokenizer st = new StreamTokenizer(new BufferedReader(
				new InputStreamReader(System.in)));

		int n, m;
		while (true) {
			st.nextToken();
			n = (int) st.nval; // 道路数目

			st.nextToken();
			m = (int) st.nval; // 村庄数目

			if (n == 0)
				break;

			int arr[][] = new int[m + 1][m + 1]; // 无穷（用很大的数代替）代表没有路，非0代表有路
			for (int i = 0; i <= m; i++)
				for (int j = 0; j <= m; j++) {
					arr[i][j] = Integer.MAX_VALUE;
				}

			UnionFindSet ufs = new UnionFindSet(m + 1);

			// 延续1012题的思路，先判断是否可以实现相通
			int n1, n2, weight, num = 0;
			for (int i = 0; i < n; i++) {
				st.nextToken();
				n1 = (int) st.nval;

				st.nextToken();
				n2 = (int) st.nval;

				st.nextToken();
				weight = (int) st.nval;

				// 去重复边？？
				if (arr[n1][n2] == 0) {
					arr[n1][n2] = weight;
					arr[n2][n1] = weight;
				} else {
					arr[n1][n2] = Math.min(arr[n1][n2], weight);
					arr[n2][n1] = Math.min(arr[n1][n2], weight);
				}

				if (ufs.find(n1) != ufs.find(n2)) {
					ufs.union(n1, n2);
					num++;
				}
			}

			if (num >= (m - 1)) { // 可以相通，求BST（prim）
				int flag[] = new int[m + 1];// 0代表该顶点不在集合U中，1代表在集合U中
				flag[1] = 1; // 从顶点1开始
				int pos = 1; // 目前的顶点

				int numedge = 0; // 代表加入TE中的边的个数
				int wei = 0; // BST的权重之和

				int min[] = new int[m + 1]; // 边的权重
				for (int i = 1; i <= m; i++) {
					min[i] = arr[pos][i];
				}

				while (true) {
					int minmin = Integer.MAX_VALUE;
					int lastpos=pos;

					for (int i = 1; i <= m; i++) {
						if (flag[i] == 0 && min[i] < minmin) {
							minmin = min[i];
							lastpos=pos;
							pos = i;
						}
					}

					flag[pos] = 1;

					for (int i = 1; i <= m; i++) {
						if (flag[i] == 0 && min[i] > arr[pos][i])
								min[i] = arr[pos][i];
					}

//					wei += arr[lastpos][pos];
					wei+=min[pos];//!!!!
					numedge++; // 名字一定要区分开使用范围，不然容易出错

					if (numedge == (m - 1))
						break;
				}

				System.out.println(wei);
			} else { // 不能相通
				System.out.println("?");
			}
		}
	}

}

class UnionFindSet {
	int set[];
	int size[];

	UnionFindSet() {

	}

	UnionFindSet(int n) {
		set = new int
;
		size = new int
;
		for (int i = 0; i < n; i++) {
			set[i] = i;
			size[i] = 1;
		}
	}

	int find(int i) {
		while (i != set[i]) {
			i = set[i];
		}
		return i;
	}

	void union(int i, int j) {
		int p = find(i);
		int q = find(j);

		if (size[p] < size[q]) {
			set[p] = q;
			size[q] += size[p]; // 勿忘修改size
		} else {
			set[q] = p;
			size[p] += size[q];
		}
	}
}