二分匹配（Hopcroft-Carp算法）

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/Game_Acm/article/details/82388692

int tol,head[maxn];
struct edge
{
    int to,next;
}es[maxm];
void addedge( int u , int v )
{
    es[tol].to = v;
    es[tol].next = head[u];
    head[u] = tol++;
}
int un,dis;
int mx[maxn],my[maxn];
int dx[maxn],dy[maxn];
bool used[maxn];
bool SearchP()
{
    dis = inf;
    queue<int>Q;
    memset ( dx , -1 , sizeof(dx) );
    memset ( dy , -1 , sizeof(dy) );
    for ( int i=0 ; i<un ; i++ )
    {
        if ( mx[i]==-1 )
        {
            dx[i] = 0;
            Q.push(i);
        }
    }
    while( !Q.empty() )
    {
        int u = Q.front(); Q.pop();
        if  ( dx[u]>dis ) break;
        for ( int i=head[u] ; i!=-1 ; i=es[i].next )
        {
            int v = es[i].to;
            if  ( dy[v]==-1 )
            {
                dy[v] = dx[u]+1;
                if ( my[v]==-1 )
                {
                    dis = dy[v];
                }
                else
                {
                    dx[my[v]] = dy[v]+1;
                    Q.push(my[v]);
                }
            }
        }
    }
    return dis!=inf;
}
bool dfs( int u )
{
    for ( int i=head[u] ; i!=-1 ; i=es[i].next )
    {
        int v = es[i].to;
        if ( !used[v]&&dy[v]==dx[u]+1 )
        {
            used[v] = true;
            if ( my[v]!=-1&&dy[v]==dis ) continue;
            if ( my[v]==-1||dfs(my[v]) )
            {
                my[v] = u;
                mx[u] = v;
                return true;
            }
        }
    }
    return false;
}
int MaxMatch()
{
    int res = 0;
    memset ( mx , -1 , sizeof(mx) );
    memset ( my , -1 , sizeof(my) );
    while ( SearchP() )
    {
        memset ( used , false , sizeof(used) );
        for ( int i=0 ; i<un ; i++ )
            if ( mx[i]==-1&&dfs(i) ) res++;
    }
    return res;
}