【HDOJ】3367 Pseudoforest

并查集。

#include <cstdio>
#include <cstring>
#include <cstdlib>

#define MAXN 10005
#define INF  0xffffff

typedef struct {
    int c, s, e;
} edge_st;

edge_st edges[100005];
int pre[MAXN];
int deg[MAXN];
int n, m, ans;

int comp(const void *a, const void *b) {
    return ((edge_st *)b)->c - ((edge_st *)a)->c;
}

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

void merge(int i) {
    int a, b;

    a = find(edges[i].s);
    b = find(edges[i].e);
    if (a != b) {
        if (deg[a] == 0) {
            pre[a] = b;
            ans += edges[i].c;
        } else if (deg[b] == 0) {
            pre[b] = a;
            ans += edges[i].c;
        }
    } else {
        if (deg[a] == 0) {
            ++deg[a];
            ans += edges[i].c;
        }
    }
}

int main() {
    int i;

    while (scanf("%d %d", &n, &m)!=EOF && (n||m)) {
        for (i=0; i<m; ++i)
            scanf("%d %d %d", &edges[i].s, &edges[i].e, &edges[i].c);
        qsort(edges, m, sizeof(edge_st), comp);
        for (i=0; i<n; ++i)
            pre[i] = i;
        memset(deg, 0, sizeof(deg));
        ans = 0;
        for (i=0; i<m; ++i)
            merge(i);
        printf("%d
", ans);
    }

    return 0;
}