POJ 2421 Constructing Roads(最小生成树)

//最小生成树//只需将已经建成的路的边权值置零即可//然后对边进行排序，建立并查集，用Kruscal#include<iostream>#include<algorithm>#include<vector>#define MAX 105using namespace std;int N,Q;int G[MAX][MAX];int fa[MAX];struct Edge{int u,v,w;Edge(int uu,int vv,int ww){u = uu;v = vv;w = ww;}};vector<Edge> E;void readGraph(){int u,v;scanf("%d",&N);for(int i = 1;i <= N;++i)for(int j = 1;j <= N;++j)scanf("%d",&G[i][j]);scanf("%d",&Q);while(Q--){scanf("%d%d",&u,&v);G[u][v] = G[v][u] = 0;}}void readEdge(){for(int i = 1;i <= N;++i)for(int j = 1;j <= N;++j){if(j == i)continue;E.push_back(Edge(i,j,G[i][j]));}}bool cmp(Edge a,Edge b){return a.w < b.w;}void initSet()//建立并查集{for(int i = 1;i <= N;++i)fa[i] = i;}int Find(int x){if(x == fa[x])return x;else return fa[x] = Find(fa[x]);//路径压缩}bool Union(int x,int y){x = Find(x);y = Find(y);if(x == y)return 0;else{fa[x] = y;return 1;}}int Kruscal(){initSet();int u,v,w,ans = 0;sort(E.begin(),E.end(),cmp);for(int i = 0;i < E.size();++i){u = E[i].u;v = E[i].v;w = E[i].w;if(Union(u,v))ans += w;}return ans;}int main(){readGraph();readEdge();printf("%d/n",Kruscal());return 0;}