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回来了！

今天（？发出来的时候可能已经是第二天了吧

真的爆零了qaq

挺难的 最高分只有100 而且t2t3t4一个人都没拿分qaq

这段时间在写网络流 唉博客还是不要写太水了 抄一点网络流代码上来

EK不写了 dinic会就行了

板子题洛谷p3376

dinic做法

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 210, M = 1e4+10;
int n, m, s, t, tot = 1, ver[M], h[N], nxt[M], edg[M], d[N], now[N], fl, inf = 0x7fffffff, maxf;
queue < int > q, clr;
void add(int u, int v, int w){ver[++tot] = v; edg[tot] = w, nxt[tot] = h[u];h[u] = tot;ver[++tot] = u; edg[tot] = 0, nxt[tot] = h[v];h[v] = tot;
}
bool bfs(){memset(d, 0, sizeof d); q = clr;q.push(s); d[s] = 1, now[s] = h[s];while (q.size()){int x = q.front(); q.pop();for (int i = h[x]; i; i = nxt[i]){if (!edg[i] || d[ver[i]]) continue;q.push(ver[i]);now[ver[i]] = h[ver[i]];d[ver[i]] = d[x] + 1;if (ver[i] == t) return true;}}return false;
}
int dinic(int x, int flw){if (x == t) return flw;int rst = flw;for (int i = now[x]; i; i = nxt[i]){now[x] = i;if (!edg[i] || d[ver[i]] != d[x] + 1) continue;int k = dinic(ver[i], min(rst, edg[i]));if (!k) d[ver[i]] = 0;edg[i] -= k; edg[i ^ 1] += k;rst -= k;}return flw - rst;
}
signed main(){ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);cin >> n >> m >> s >> t;for (int i = 1; i <= m; ++i){int u, v, w; cin >> u >> v >> w;add(u, v, w);}while (bfs()) while (fl = dinic(s, inf)) maxf += fl;cout << maxf << "\n";return 0;
}

dinic优化ISAP做法

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N = 210, M = 1e4+10;
int n, m, s, t, tot = 1, ver[M], h[N], nxt[M], edg[M], dep[N], gap[N], maxf, inf = 0x7fffffff, cur[N];
queue < int > q;
void add(int u, int v, int w){ver[++tot] = v; nxt[tot] = h[u], edg[tot] = w;h[u] = tot;ver[++tot] = u; nxt[tot] = h[v], edg[tot] = 0;h[v] = tot; 
}
void bfs(){memset(dep, -1, sizeof(dep));q.push(t); gap[dep[t] = 0] = 1;while (!q.empty()){int x = q.front(); q.pop();for (int i = h[x]; i; i = nxt[i]){if (dep[ver[i]] != -1) continue;q.push(ver[i]); dep[ver[i]] = dep[x] + 1;++gap[dep[ver[i]]];}}
}
int dfs(int x, int flw){if (x == t) return flw;int rst = flw;for (int i = cur[x]; i; i = nxt[i]){cur[x] = i;if (!edg[i] || dep[ver[i]] != dep[x] - 1) continue;int k = dfs(ver[i], min(rst, edg[i]));edg[i] -= k, edg[i ^ 1] += k;rst -= k;if (!rst) return flw;} --gap[dep[x]];if (!gap[dep[x]]) dep[s] = n + 1;++gap[++dep[x]];return flw - rst;
}
int isap(){bfs();while (dep[s] < n){memcpy(cur, h, sizeof(cur));maxf += dfs(s, inf);}return maxf;
}
signed main(){ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);cin >> n >> m >> s >> t;for (int i = 1; i <= m; ++i){int u, v, w; cin >> u >> v >> w;add(u, v, w);}cout << isap() << "\n";return 0;
}

费用流板子题洛谷p3381

dinic+spfa

#include<bits/stdc++.h>
//#define int long long
using namespace std;
const int N = 5010, M = 200010, inf = 0x3f3f3f3f;
int m, n, k, tot = 1, h[N], ver[M], nxt[M], edg[M], cst[M], dis[N], cur[N], s, t, ans, maxf, fl;
bool vis[N], v[N];
queue < int > q, clr;
void add(int u, int v, int w, int c){ver[++tot] = v; nxt[tot] = h[u], edg[tot] = w, cst[tot] = c;h[u] = tot;ver[++tot] = u; nxt[tot] = h[v], edg[tot] = 0, cst[tot] = -c;h[v] = tot;
}
bool spfa(){q = clr;memset(dis, 0x3f, sizeof(dis));memset(vis, 0, sizeof vis);q.push(s); dis[s] = 0, vis[s] = 1;while (q.size()){int x = q.front(); q.pop(); vis[x] = 0;for (int i = h[x]; i; i = nxt[i]){if (!edg[i] || dis[ver[i]] <= dis[x] + cst[i]) continue;dis[ver[i]] = dis[x] + cst[i];if (!vis[ver[i]]) vis[ver[i]] = 1, q.push(ver[i]);}}return dis[t] != inf;
}
int dinic(int x, int flw){v[x] = 1;if (x == t) return flw;int rst = flw;for (int i = cur[x]; i; i = nxt[i]){cur[x] = i;if (!edg[i] || dis[ver[i]] != dis[x] + cst[i] || v[ver[i]]) continue; v[ver[i]] = 1;int k = dinic(ver[i], min(rst, edg[i]));edg[i] -= k, edg[i ^ 1] += k;rst -= k; ans += k * cst[i];}return flw - rst;
}
signed main() {//ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);cin >> n >> m >> s >> t;for (int i = 1; i <= m; ++i){int u, v, w, c; cin >> u >> v >> w >> c;add(u, v, w, c);}while (spfa()){memcpy(cur, h, sizeof(h));memset(v, 0, sizeof(v));while ((fl = dinic(s, inf)) > 0) maxf += fl;}cout << maxf << " " << ans << "\n";return 0;
}

其他一些例题 不放代码了

洛谷p4452 

洛谷p2053

洛谷p2045

如果有可能说不定到时候会写网络流学习笔记...?（大概率是不可能的