最小生成树 || HDU 1301 Jungle Roads

Posted 2020-10-23 舒羽倾

裸的最小生成树

输入很蓝瘦

**并查集

int find(int x) { return x == fa[x] ? x : fa[x] = find(fa[x]); }

找到x在并查集里的根结点，如果两个端点在同一个集合内，find之后两个值就相等了

每次找到权值最小的端点不在同一集合的边 把两个集合合并

#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
int fa[33];
struct node
{
    int s, e, d;
}l[111];
bool cmp(node x, node y)
{
    if(x.d != y.d) return x.d < y.d;
}
int find(int x)
{
    return x == fa[x] ? x : fa[x] = find(fa[x]);
}
int main()
{
    while(1)
    {
        int n, i, j, x, val, sum = 0, cnt = 0;//cnt是边数
        char c;
        scanf("%d", &n);
        if(n == 0) break;
        for(i = 0; i < n - 1; i++)
        {
            scanf(" %c", &c);
            int s = c - ‘A‘ + 1;
            scanf("%d", &x);
            for(j = 0; j < x; j++)
            {
                scanf(" %c %d", &c, &val);
                int e = c - ‘A‘ + 1;
                l[cnt++] = (node){s, e, val};
            }
        }
        sort(l, l + cnt, cmp);
        for(int i = 1; i <= n; i++)
            fa[i] = i;
        for(int i = 0; i < cnt; i++)
        {
            int fs = find(l[i].s), fe = find(l[i].e);
            if(fs == fe) continue;
            sum += l[i].d;
            fa[fs] = fe;
        }
        printf("%d\n", sum);
    }
    return 0;
}