bfs寻找增广路

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<string>
#include<queue>
#include<stack>
#include<vector>
#include<cstdlib>
#include<map>
#include<cmath>
using namespace std;

const int maxn = 600;

struct E{
int u,v,use;
E () {use = 0;}
}edgs[2*maxn];

struct EP{
int v,p;
};

int n,i,j,fa[4*maxn],num[4*maxn],cur = 0,From[2*maxn],visp[4*maxn];
bool ok[2*maxn],vis[2*maxn],r[2*maxn];

vector <EP> vp[4*maxn];
vector <int> ve[2*maxn];
queue <int> q;

int father (int k)
{
return k == fa[k]?k:fa[k] = father(fa[k]);
}

bool Insert (int x)
{
int fu = father(edgs[x].u);
int fv = father(edgs[x].v);
if (fu == fv) return false;
fa[fu] = fv;
edgs[x].use = 1;
return true;
}

bool dfs (int now,int to,int sy)
{
if (now == to) return true;
visp[now] = sy;
for (int l = 0; l < vp[now].size(); l++)
{
int To = vp[now][l].v;
if (visp[To] == sy) continue;
int Num = vp[now][l].p;
r[Num] = true;
if (dfs(To,to,sy)) return true;
r[Num] = false;
}
return false;
}

void Build (int x)
{
int l;
memset(ok,false,sizeof(ok));
memset(r,-1,sizeof(r));
memset(visp,-1,sizeof(visp));
for (l = 0; l <= x; l++) ve[l].push_back(l^1);
for (l = 0; l <= x; l++)
if (!edgs[l].use)
{
ok[l] = true;
memset(r,false,sizeof(r));
if (!dfs(edgs[l].u,edgs[l].v,l)) continue;
ok[l] = false;
for (j = 0; j < x; j++) if (r[j]) ve[l].push_back(j);
}
}

bool bfs (int x)
{
memset(vis,false,sizeof(vis));
memset(From,-1,sizeof(From));
int end = -1;
q.push(x);
vis[x] = true;
while (!q.empty())
{
int k = q.front();
q.pop();
for (int l = 0; l < ve[k].size(); l++)
{
int To = ve[k][l];
if (vis[To]) continue;
vis[To] = true;
if ((edgs[To].use ^ edgs[k].use))
{
From[To] = k;
if (ok[To])
{
end = To;
while (!q.empty()) q.pop();
break;
}
q.push(To);
}
}
}
if (end == -1) return false;
for (; end != -1; end = From[end]) edgs[end].use ^= 1;
return true;
}

void Clear()
{
for (j = 0; j <= cur; j++) fa[j] = j;
for (j = 0; j < 4*n; j++) vp[j].clear();
for (j = 0; j < 2*n; j++) ve[j].clear();
for (j = 0; j < 2*i; j++)
if (edgs[j].use)
{
fa[father(edgs[j].u)] = father(edgs[j].v);
vp[edgs[j].u].push_back((EP){edgs[j].v,j});
vp[edgs[j].v].push_back((EP){edgs[j].u,j});
}
}

int main()
{
#ifndef ONLINE_JUDGE
#ifndef YZY
freopen("game.in","r",stdin);
freopen("game.out","w",stdout);
#else
freopen("yzy.txt","r",stdin);
#endif
#endif
cin >> n;
j = -1;
for (i = 0; i < 2*n; i++)
{
scanf("%d%d",&edgs[i].u,&edgs[i].v);
num[++j] = edgs[i].u;
num[++j] = edgs[i].v;
}
sort (num,num + j + 1);
for (i = 1; i <= j; i++)
if (num[i] != num[i-1])
num[++cur] = num[i];
for (i = 0; i < 2*n; i++)
{
edgs[i].u = lower_bound(num,num + cur + 1,edgs[i].u) - num;
edgs[i].v = lower_bound(num,num + cur + 1,edgs[i].v) - num;
}
for (i = 0; i < n; i++)
{
Clear();
if (Insert(2*i)) continue;
if (Insert(2*i+1)) continue;
Build(2*i+1);
if (bfs(2*i)) continue;
bfs(2*i+1);
}
int ans = 0;
for (i = 0; i < 2*n; i++)
if (edgs[i].use)
++ans;
cout << ans;
return 0;
}