poj1251 Jungle Roads

poj1251 Jungle Roads

标签：最小生成树

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题目链接

/*
    题意：输出最小生成树的权值和。每组数据给出节点个数n，以下n-1行，
          开头为起始节点，及与它相连的节点数目m，随后m组数据表示和它相连的节点以及边权值(用c++处理空格和换行符)。
    思路：Kruskal。
*/
#include <stdio.h>
#include <iostream>
#include <algorithm>
using namespace std;

#define maxn 30

typedef struct{
    int x, y;
    int w;
}edge;

edge e[maxn * maxn / 2];
int rank_[maxn], father[maxn], sum;

int cmp(edge a, edge b){  //
    return a.w < b.w;
}

void make_set(int x){
    father[x] = x;
    rank_[x] = 0;
}

int find_set(int x){
    return  x != father[x] ? find_set(father[x]) : father[x];
}

void union_set(int x, int y, int w){
    if(x == y)  return ;
    if(rank_[x] > rank_[y])  father[y] = x;
    else{
        if(rank_[x] == rank_[y])  rank_[y]++;
        father[x] = y;
    }
    sum += w;  //
}

int main(){
    int n, m, k, weight, i, j;
    char a, b;

    while(scanf("%d", &n) && n){
        k = 0, sum = 0;
        for(i = 0; i < n - 1; i++){
            cin >> a >> m, make_set(a - 'A');
            for(j = 0; j < m; j++){
                cin >> b >> weight, make_set(b - 'A');
                e[k].x = a - 'A', e[k].y = b - 'A';
                e[k++].w = weight;
            }
        }
        sort(e, e + k, cmp);
        for(i = 0; i < k; i++)  union_set(find_set(e[i].x), find_set(e[i].y), e[i].w);
        printf("%d\n", sum);
    }

    return 0;
}