Ural 1416 confidential, sub-generated tree

Not strictly generate small trees.

Note that the graph may not be connected.

#include <cstdio>#include <cstring>#include <algorithm>#include <vector>using namespace std;const int maxn = 505;const int INF = 1e7;bool vis[maxn];int d[maxn];int pre[maxn];int Max[maxn][maxn];int g[maxn][maxn];int n, m;void init(){    int u, v, c;    scanf("%d%d", &n, &m);    for(int i=1; i<=n; ++i) for(int j=1; j<=n; ++j) g[i][j] = INF;    for(int i=1; i<=m; ++i) {        scanf("%d%d%d", &u, &v, &c);        g[u][v] = g[v][u] = c;    }}int Prim(){    for(int i=2; i<=n; ++i) {        pre[i]=1;        d[i] = g[1][i];    }    memset(vis, 0, sizeof vis );    vis[1] = 1; d[1] = 0; pre[1] = -1;    int ans = 0;    for(int i=1; i<n; ++i) {        int Mn = INF, k = -1;        for(int j=1; j<=n; ++j)            if(!vis[j] && Mn>d[j]){ Mn = d[k=j];}        if(-1==k) return INF;        ans += Mn;        g[k][pre[k]] = g[pre[k]][k] = INF;        for(int j=1; j<=n; ++j) if(vis[j])                Max[j][k] = Max[k][j] = max(Mn, Max[pre[k]][j]);        vis[k] = 1;        for(int j=1; j<=n; ++j)            if(!vis[j]&&d[j]>g[j][k]) {                d[j] = g[j][k];                pre[j] = k;            }    }    return ans;}void solve(){    int ans1 = Prim();    if(ans1==INF) {        printf("Cost: -1\n");    } else {        printf("Cost: %d\n", ans1);    }    int ans2 = INF;    for(int i=1; i<=n; ++i)        for(int j=i+1; j<=n; ++j)            if(g[i][j]!=INF) {                ans2 = min(ans2, ans1+g[i][j]-Max[i][j]);            }    if(ans2==INF){        printf("Cost: -1\n");    } else {        printf("Cost: %d\n", ans2);    }}int main(){    init();    solve();    return 0;}

Ural 1416 confidential, sub-generated tree