【luogu P3959 宝藏】 题解

题目链接：https://www.luogu.org/problemnew/show/P3959

我只是心血来潮想学SA（考场上骗分总行吧）。

这个题可以状压DP、爆搜+剪枝、有意思的还是随机化搜索（是的，这个题用的不叫SA，没有降温）。

code：

#include <queue>
#include <ctime>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 10000;
const int inf = 0x7fffffff;
int ma[13][13], deep[maxn], n, m, ans;
struct edge{
	int u, v;
};
bool operator < (struct edge a, struct edge b)
{
	return deep[a.u] * ma[a.u][a.v] > deep[b.u] * ma[b.u][b.v];
}
int sear(int s)//s 起点
{
	int cnt = 0, cost = 0;
	bool vis[maxn];
	edge e[maxn], now, now2;
	priority_queue<edge> q;
	memset(deep, 0, sizeof(deep));
	memset(vis, 0, sizeof(vis));
	deep[s] = 1, vis[s] = 1;
	for(int i = 1; i <= n; i++)
	if(ma[s][i] < inf)
	{
		now.u = s, now.v = i;
		//cout<<now.u<<" "<<now.v<<endl;
		q.push(now);
	}
	for(int i = 1; i <= n-1; i++)
	{
		now = q.top(); q.pop();
		while(!q.empty() && ((vis[now.v] || rand()%(n) < 1)))
		{
			if(!vis[now.v]) e[++cnt] = now;
			now = q.top(); q.pop();
		}
		vis[now.v] = 1, deep[now.v] = deep[now.u] + 1;
		//cout<<cnt;
		for(int i = 1; i <= cnt; i++) q.push(e[i]);
		for(int i = 1; i <= n; i++)
		{
			if(ma[now.v][i] != inf && !vis[i])
			{
				now2.u = now.v; now2.v = i;

				q.push(now2);
			}
		}
		cost += ma[now.u][now.v] * deep[now.u];
	}
	return cost;
}
int main()
{
	scanf("%d%d",&n,&m);
	for(int i = 1; i <= n; i++)
		for(int j = 1; j <= n; j++) ma[i][j] = inf;
	for(int i = 1; i <= m; i++)
	{
		int u, v, w;
		scanf("%d%d%d",&u,&v,&w);
		ma[u][v] = min(w, ma[u][v]);
		ma[v][u] = min(w, ma[v][u]);
	}
	srand(192608);
	ans = inf;

	for(int i = 1; i <= 500; i++)
	{
		for(int j = 1; j <= n; j++)
		ans = min(ans, sear(j));
	}
	printf("%d",ans);
	return 0;
}