poj 2421 Constructing Roads (Kruskal)

#include <iostream>#include <cstring>#include <cstdio>using namespace std;const int MAXM = 10050;const int MAXN = 110;struct Edge{int u, v, w;};Edge edges[MAXM];int parent[MAXN];int n, m;void UFset(){int i;for(i = 0; i < n; ++i){parent[i] = -1;}}int Find_Parent(int x){int s;for (s = x; parent[s] >= 0; s = parent[s]);while(s != x){int tmp = parent[x];parent[x] = s;x = tmp;}return s;}void Union(int u, int v){int r1 = Find_Parent( u );int r2 = Find_Parent( v );int tmp = parent[r1] + parent[r2];if (parent[r1] > parent[r2]){parent[r1] = r2;parent[r2] = tmp;}else{parent[r2] = r1;parent[r1] = tmp;}}int Kruskal(){int i;int sum = 0;int u, v;UFset();int num = 0;for (i = 0; i < m; ++i){u = edges[i].u;v = edges[i].v;if (Find_Parent(u) != Find_Parent(v)){sum += edges[i].w;num++;Union(u, v);}if(num >= n-1)break;}return sum;}int cmp(const void* a, const void* b){Edge* aa = (Edge *)a;Edge* bb = (Edge *)b;if(aa->w > bb->w)return 1;elsereturn -1;}int main(){int sum;int M[MAXN][MAXN];int flag[MAXN][MAXN];int i, j;int Q, a, b;while(~scanf("%d", &n)){int mi = 0;memset(flag, 0, sizeof(flag));for (i = 0; i < n; ++i){for (j = 0; j < n; ++j){cin>>M[i][j];}}cin>>Q;for(i = 0; i < Q; ++i){cin>>a>>b;flag[a-1][b-1] = 1;}for (i = 0; i < n; ++i){for (j = i+1; j < n; ++j){if(flag[i][j]){edges[mi].u = i;edges[mi].v = j;edges[mi++].w = 0;}else{edges[mi].u = i;edges[mi].v = j;edges[mi++].w = M[i][j];}}}m = mi;qsort(edges, m, sizeof(edges[0]), cmp);sum = Kruskal();cout<<sum<<endl;}return 0;}