HDU2426 Interesting Housing Problem（KM匹配 ）

题意：N个学生安排到M个宿舍，每个学生对宿舍有个评价，正数，0，负数，现在评价是负数的，不能让这个学生去这个房间，问怎么安排让所有的学生都住进宿舍且评价最大。
思路：建立图的权重时，筛选掉负数边。

#include<cstdio>#include<iostream>#include<algorithm>#include<cmath>#include<set>#include<map>#include<string>#include<cstring>#include<stack>#include<queue>#include<vector>#include<cstdlib>#define lson (rt<<1),L,M#define rson (rt<<1|1),M+1,R#define M ((L+R)>>1)#define cl(a,b) memset(a,b,sizeof(a));#define LL long long#define P pair<int,int>#define X first#define Y second#define pb push_back#define fread(zcc)  freopen(zcc,"r",stdin)#define fwrite(zcc) freopen(zcc,"w",stdout)using namespace std;const int maxn=505;const LL inf=9999999999;LL w[maxn][maxn];int linker[maxn],lx[maxn],ly[maxn],slack[maxn];bool visx[maxn],visy[maxn];int nx,ny;bool dfs(int x){    visx[x]=true;    for(int y=0;y<ny;y++)if(w[x][y]>=0){///边的限制        if(visy[y])continue;        int tmp=lx[x]+ly[y]-w[x][y];        if(tmp==0){            visy[y]=true;            if(linker[y]==-1||dfs(linker[y])){                linker[y]=x;                return true;            }        }        else if(slack[y]>tmp){            slack[y]=tmp;        }    }    return false;}LL km(){    cl(linker,-1);    cl(ly,0);    for(int i=0;i<nx;i++){        lx[i]=-inf;        for(int j=0;j<ny;j++)if(w[i][j]>lx[i]){            lx[i]=w[i][j];        }    }    for(int x=0;x<nx;x++){        fill(slack,slack+ny+1,inf);        while(true){            cl(visx,false);            cl(visy,false);            if(dfs(x))break;            int d=inf;            for(int i=0;i<ny;i++)if(!visy[i]&&d>slack[i]){                d=slack[i];            }            for(int i=0;i<nx;i++)if(visx[i]){                lx[i]-=d;            }            for(int i=0;i<ny;i++)if(visy[i])ly[i]+=d;            else slack[i]-=d;        }    }    LL ans=0;    cl(visx,false);///用于下面判断每个学生是不是都安排了住宿    for(int i=0;i<ny;i++)if(linker[i]!=-1){//注意循环的上限是ny        ans+=w[linker[i]][i];        visx[linker[i]]=true;    }    for(int i=0;i<nx;i++)if(visx[i]==0)return -1;//检查每个学生是不是都安排了宿舍    return ans;}int main(){    int cas=1;    int n,m,e;    while(~scanf("%d%d%d",&n,&m,&e)){        if(e==0){             printf("Case %d: -1\n",cas++);             continue;        }        cl(w,-1);        bool ok=true;        while(e--){            int s,r,v;            scanf("%d%d%d",&s,&r,&v);            if(v>=0)w[s][r]=v;//不要负数的边        }        nx=n;ny=m;        LL ans=km();        printf("Case %d: %lld\n",cas++,ans);    }    return 0;}