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  • UVA-10600.Contest and Blackout.(Kruskal + 次小生成树)

    题目链接

    本题思路:模版的次小生成树问题,输出MST and Second_MST的值。

    参考代码:

    #include <cstdio>
    #include <cstring>
    #include <algorithm>
    #include <cstring>
    #include <vector>
    using namespace std;
    
    const int maxn = 100 + 5, maxe = 100 * 100 / 2 + 5, INF = 0x3f3f3f3f;
    int n, m, Max[maxn][maxn], pir[maxn];
    struct Edge {
        int u, v, w;
        bool vis;
    }edge[maxe];
    vector<int> G[maxn];
    
    bool cmp(const Edge &a, const Edge &b) {
        return a.w < b.w;
    }
    
    int Find(int x) {
        if(x == pir[x]) return x;
        return pir[x] = Find(pir[x]);
    }
    
    int Kruskal() {
        sort(edge + 1, edge + m + 1, cmp);
        for(int i = 1; i <= n; i ++) {
            G[i].clear();
            pir[i] = i;
            G[i].push_back(i);
        }
        int cnt = 0, ans = 0;
        for(int i = 1; i <= m; i ++) {
            int fx = Find(edge[i].u), fy = Find(edge[i].v);
            if(cnt == n - 1) break;
            if(fx != fy) {
                cnt ++;
                int len_fx = G[fx].size(), len_fy = G[fy].size();
                edge[i].vis = true;
                ans += edge[i].w;
                for(int j = 0; j < len_fx; j ++) {
                    for(int k = 0; k < len_fy; k ++) {
                        Max[G[fx][j]][G[fy][k]] = Max[G[fy][k]][G[fx][j]] = edge[i].w;
                    }
                }
                pir[fx] = fy;
                for(int j = 0; j < len_fx; j ++)
                    G[fy].push_back(G[fx][j]);
            }
        }
        if(cnt < n - 1) return INF;
        else return ans;
    }
    
    int Second_Kruskal(int MST) {
        int ans = INF;
        for(int i = 1; i <= m; i ++) {
            if(!edge[i].vis)
                ans = min(ans, MST + edge[i].w - Max[edge[i].u][edge[i].v]);
        }
        return ans;
    }
    
    int main () {
        int t;
        scanf("%d", &t);
        while(t --) {
            scanf("%d %d", &n, &m);
            for(int i = 1; i <= m; i ++) {
                scanf("%d %d %d", &edge[i].u, &edge[i].v, &edge[i].w);
                edge[i].vis = false;
            }
            int MST = Kruskal();
            int Second_MST = Second_Kruskal(MST);
            printf("%d %d
    ", MST, Second_MST);
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/bianjunting/p/10837618.html
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