【最小生成树】

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/*本题要求求出最大树，刚好克鲁斯卡尔算法按照权值从大到小排序就行了POJ  2377*/#include<cstdio>#include<algorithm>using namespace std;int father[1005];int n,m;struct Edge{    int s,e;    int cost;}edge[20005];int cmp(Edge x,Edge y){    return x.cost>y.cost;}void make_set(){    for(int i=1;i<=n;i++)        father[i]=i;    for(int i=1;i<m;i++)        edge[i].cost=0;}int find_set(int x){    if(x!=father[x])        father[x]=find_set(father[x]);    return father[x];}int union_set(int x,int y){    int fx=find_set(x);    int fy=find_set(y);    if(fx==fy)        return 0;    father[fx]=fy;    return 1;}int main(){    while(~scanf("%d%d",&n,&m)){        int sum=0;         make_set();        for(int i=0;i<m;i++){            scanf("%d%d%d",&edge[i].s,&edge[i].e,&edge[i].cost);        }        sort(edge,edge+m,cmp);        for(int i=0;i<m;i++){            if(union_set(edge[i].s,edge[i].e)){                sum+=edge[i].cost;            }        }        int a=find_set(1),flag=1;        for(int i=2;i<=n;i++){            if(find_set(i)!=a){                flag=0;                break;            }        }        if(flag)            printf("%d\n",sum);        else            printf("-1\n");    }}

/*求最小生成树中的最长边POJ  2395*/#include<cstdio>#include<algorithm>using namespace std;int father[2005];int n,m;struct Edge{    int s,e;    int cost;}edge[10005];int cmp(Edge x,Edge y){    return x.cost<y.cost;}void make_set(){    for(int i=1;i<=n;i++)        father[i]=i;    for(int i=1;i<m;i++)        edge[i].cost=0;}int find_set(int x){    if(x!=father[x])        father[x]=find_set(father[x]);    return father[x];}int union_set(int x,int y){    int fx=find_set(x);    int fy=find_set(y);    if(fx==fy)        return 0;    father[fx]=fy;    return 1;}int main(){    while(~scanf("%d%d",&n,&m)){         make_set();        for(int i=0;i<m;i++){            scanf("%d%d%d",&edge[i].s,&edge[i].e,&edge[i].cost);        }        sort(edge,edge+m,cmp);        int max_x=-1;        for(int i=0;i<m;i++){            if(union_set(edge[i].s,edge[i].e)){                if(max_x<edge[i].cost)                    max_x=edge[i].cost;            }        }       printf("%d\n",max_x);    }}

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