[BZOJ 2180]最小直径生成树

最小直径生成树

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#define maxn 210using namespace std;const int inf = 0x7fffffff / 2;int n, m;int f[maxn][maxn], d[maxn][maxn], p[maxn][maxn];void MST(){//Floydfor(int k = 1; k <= n; k ++)    for(int i = 1; i <= n; i ++)        for(int j = 1; j <= n; j ++)            if(i != j && j != k && k != i)                f[i][j] = min(f[i][j], f[i][k] + f[k][j]);                //getrankfor(int i = 1; i <= n; i ++){for(int j = 1; j <= n; j ++)    p[i][j] = j;for(int j = 1; j <= n; j ++)for(int k = j + 1; k <= n; k ++)    if(f[i][p[i][j]] > f[i][p[i][k]])        swap(p[i][j], p[i][k]);}//mainint ans = inf;for(int u = 1; u <= n; u ++){for(int v = 1; v <= n; v ++){if(d[u][v] != inf){ans = min(ans, min(f[u][p[u][n]] << 1, f[v][p[v][n]] << 1));int t = n;for(int k = n - 1; k >= 1; k --){if(f[v][p[u][t]] < f[v][p[u][k]]){ans = min(ans, f[u][p[u][k]] + f[v][p[u][t]] + d[u][v]);t = k;}}}}}printf("%d\n", ans);}int main(){scanf("%d%d", &n, &m);for(int i = 1; i <= n; i ++)for(int j = 1; j <= n; j ++)f[i][j] = d[i][j] = inf;for(int i = 1; i <= n; i ++)    f[i][i] = d[i][i] = 0;int u, v, dis;for(int i = 1; i <= m; i ++){scanf("%d%d%d", &u, &v, &dis);f[u][v] = f[v][u] = d[u][v] = d[v][u] = dis;}MST();    return 0;}