POJ2377 Bad Cowtractors(最大生成树)

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题意：

连接农场，要求输出最大权值和并且不能连成环，如果不能全部连接，输出-1

要点;

就是最小生成树变成最大罢了，Kruskal算法，排序改成从大到小，一次AC。

15347152Seasonal2377Accepted412K63MSC++881B2016-04-03 13:27:46

#include<stdio.h>#include<stdlib.h>#include<string.h>#include<algorithm>#define maxn 100050using namespace std;int p[maxn];int m, n;struct edge{int u, v, len;}e[maxn];bool cmp(edge a, edge b){return a.len > b.len;}void init(){for (int i = 1; i <= m; i++)p[i] = i;}int find(int x){if (p[x] == x) return x;return p[x] = find(p[x]);}bool merge(int x, int y){x = find(x);y = find(y);if (x != y){p[x] = y;return true;}return false;}int kruskal(){init();sort(e, e + n, cmp);int sum = 0, edges = 0;for (int i = 0; i < n; i++){if (merge(e[i].u, e[i].v)){sum += e[i].len;edges++;}if (edges + 1 == m)return sum;}return -1;}int main(){while (~scanf("%d%d", &m, &n)){for (int i = 0; i < n; i++)scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].len);printf("%d\n", kruskal());}return 0;}

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