ural-1099-Work Scheduling(裸带花树)

// File MAXName: 1099.cpp
// Author: Zlbing
// Created Time: 2013/8/31 14:37:38

#include<iostream>
#include<string>
#include<algorithm>
#include<cstdlib>
#include<cstdio>
#include<set>
#include<map>
#include<vector>
#include<cstring>
#include<stack>
#include<cmath>
#include<queue>
using namespace std;
#define CL(x,v); memset(x,v,sizeof(x));
#define INF 0x3f3f3f3f
#define LL long long
#define REP(i,r,n) for(int i=r;i<=n;i++)
#define RREP(i,n,r) for(int i=n;i>=r;i--)
#define MAXN 250
#define SET(a,b) memset(a,b,sizeof(a))
deque<int> Q;
//g[i][j]存放关系图：i,j是否有边,match[i]存放i所匹配的点
//建图开始初始化g
//最终匹配方案为match
//复杂度O(n^3)
//点是从1到n的
bool g[MAXN][MAXN],inque[MAXN],inblossom[MAXN],inpath[MAXN];
int match[MAXN],pre[MAXN],base[MAXN];

//找公共祖先
int findancestor(int u,int v)
{
memset(inpath,false,sizeof(inpath));
while(1)
{
u=base[u];
inpath[u]=true;
if(match[u]==-1)break;
u=pre[match[u]];
}
while(1)
{
v=base[v];
if(inpath[v])return v;
v=pre[match[v]];
}
}

//压缩花
void reset(int u,int anc)
{
while(u!=anc)
{
int v=match[u];
inblossom[base[u]]=1;
inblossom[base[v]]=1;
v=pre[v];
if(base[v]!=anc)pre[v]=match[u];
u=v;
}
}

void contract(int u,int v,int n)
{
int anc=findancestor(u,v);
SET(inblossom,0);
reset(u,anc);reset(v,anc);
if(base[u]!=anc)pre[u]=v;
if(base[v]!=anc)pre[v]=u;
for(int i=1;i<=n;i++)
if(inblossom[base[i]])
{
base[i]=anc;
if(!inque[i])
{
Q.push_back(i);
inque[i]=1;
}
}
}

bool bfs(int S,int n)
{
for(int i=0;i<=n;i++)pre[i]=-1,inque[i]=0,base[i]=i;
Q.clear();Q.push_back(S);inque[S]=1;
while(!Q.empty())
{
int u=Q.front();Q.pop_front();
for(int v=1;v<=n;v++)
{
if(g[u][v]&&base[v]!=base[u]&&match[u]!=v)
{
if(v==S||(match[v]!=-1&&pre[match[v]]!=-1))contract(u,v,n);
else if(pre[v]==-1)
{
pre[v]=u;
if(match[v]!=-1)Q.push_back(match[v]),inque[match[v]]=1;
else
{
u=v;
while(u!=-1)
{
v=pre[u];
int w=match[v];
match[u]=v;
match[v]=u;
u=w;
}
return true;
}
}
}
}
}
return false;
}

int solve(int n)
{
SET(match,-1);
int ans=0;
for(int i=1;i<=n;i++)
if(match[i]==-1&&dfs(i,n))
ans++;
return ans;
}

int main()
{
int n;
while(~scanf("%d",&n))
{
int a,b;
while(~scanf("%d%d",&a,&b))
{
g[a][b]=g[b][a]=1;
}
int ans=solve(n);
printf("%d\n",ans*2);
for(int i=1;i<=n;i++)
{
if(match[i]!=-1)
{
printf("%d %d\n",i,match[i]);
match[match[i]]=-1;
match[i]=-1;
}
}
}
return 0;
}