# Luogu P3959 treasure (simulated annealing)

## meaning of the title

It's a long topic... See for yourself..

## Sol

I thought of an annealing idea. I didn't expect to pay 85 for the first time. I gave it back several times. Ha ha ha

First remove the useless edges, and then sort the remaining edges from small to large

In this way, we get a sequence of edge selection. We ask the answer to be forced to follow this sequence

Two points are selected for each annealing.

Enumerate each point to determine whether the answer can be updated,

Time complexity \$O(200 * 1000 * N * M)\$

```/*
*/
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<cstring>
#include<algorithm>
#include<vector>
#define Pair pair<int, int>
#define MP(x, y) make_pair(x, y)
#define fi first
#define se second
using namespace std;
const int MAXN = 1001;
const double eps = 1e-10, Dlt = 0.97, INF = 1e9 + 7;
char c = getchar(); int x = 0, f = 1;
while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
return x * f;
}
int N, M;
struct Edge {
int u, v, w;
bool operator < (const Edge &rhs) const {
return w < rhs.w;
}
}E[MAXN];
void unionn(int x, int y) {
fa[x] = y;
}
int find(int x) {
if(fa[x] == x) return fa[x];
else return fa[x] = find(fa[x]);
}
vector<Pair> v[MAXN];
int dfs(int x, int cnt, int fa) {
int ans = 0;
for(int i = 0; i < v[x].size(); i++) {
int to = v[x][i].fi, w = v[x][i].se;
if(to != fa) ans += dfs(to, cnt + 1, x) + w * cnt;
}
return ans;
}
int solve() {
int cur = INF, tot = 0, base = 0;
for(int i = 1; i <= N; i++) fa[i] = i, v[i].clear();
for(int i = 1; i <= M; i++) {
int x = E[i].u, y = E[i].v;
int fx = find(x), fy = find(y);
if(fx == fy) continue;
tot++; unionn(fx, fy);
v[x].push_back(MP(y, E[i].w));
v[y].push_back(MP(x, E[i].w));
}
if(tot != N - 1) return INF;
for(int i = 1; i <= N; i++)
cur = min(cur, dfs(i, 1, 0));
return cur;
}
int main() {
//    freopen("testdata.in", "r", stdin);
srand((unsigned)time(NULL));
if(N == 1) {
puts("0"); return 0;
}
for(int i = 1; i <= M; i++) {
}
for(int i = 1; i <= N; i++)
for(int j = i + 1; j <= N; j++)
E[++num] = (Edge) {i, j, link[i][j]};
sort(E + 1, E + num + 1);
int ans = solve();
int times = 200;
while(times--) {
int now = INF;
for(double T = 100000; T > eps; T *= Dlt) {
int x = rand() % num + 1, y = rand() % num + 1;
//check(x, y);
swap(E[x], E[y]);
int nxt = solve();
if(nxt < ans) {ans = nxt; continue;}
if(nxt < now || ((exp(now - nxt / T) < rand() / RAND_MAX))) {now = nxt; continue;}
swap(E[x], E[y]);
}
}
printf("%d", ans);
return 0;
}
/*
4
0 0
0 5000
2354 10000
8787 0
*/```

Keywords: C++

Added by WickedStylis on Wed, 01 Jan 2020 23:09:15 +0200