P2057 [SHOI2007]善意的投票

思路

简单的最小割模型
最小割的模型就是选出一些边，把点集划分成S和T两个部分，使得代价最小
到这题上就是板子了

代码

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;
const int MAXN = 1000;
const int INF = 0x3f3f3f3;
int n,m;
struct Edge{
    int u,v,cap,flow;
};
vector<Edge> edges;
vector<int> G[MAXN];
void addedge(int u,int v,int cap){
    edges.push_back((Edge){u,v,cap,0});
    edges.push_back((Edge){v,u,0,0});
    int cnt=edges.size();
    G[u].push_back(cnt-2);
    G[v].push_back(cnt-1);   
}
int cur[MAXN],vis[MAXN],dep[MAXN],s,t;
int dfs(int x,int a){
    if(x==t||a==0)
        return a;
    int flow=0,f=0;
    for(int &i=cur[x];i<G[x].size();i++){
        Edge &e = edges[G[x][i]];
        if(dep[e.v]==dep[x]+1&&(f=dfs(e.v,min(a,e.cap-e.flow)))>0){
            e.flow+=f;
            edges[G[x][i]^1].flow-=f;
            a-=f;
            flow+=f;
            if(!a)
                break;
        }
    }
    return flow;
}
queue<int> q;
bool bfs(void){
    memset(vis,0,sizeof(vis));
    q.push(s);
    vis[s]=true;
    dep[s]=0;
    while(!q.empty()){
        int x=q.front();
        q.pop();
        for(int i=0;i<G[x].size();i++){
            Edge &e = edges[G[x][i]];
            if(e.cap>e.flow&&(!vis[e.v])){
                vis[e.v]=true;
                dep[e.v]=dep[x]+1;
                q.push(e.v);
            }
        }
    }
    return vis[t];
}
int dinic(void){
    int flow=0;
    while(bfs()){
        memset(cur,0,sizeof(cur));
        flow+=dfs(s,INF);
    }
    return flow;
}
int main(){
    s=MAXN-2;
    t=MAXN-3;
    scanf("%d %d",&n,&m);
    for(int i=1;i<=n;i++){
        int x;
        scanf("%d",&x);
        if(x)
            addedge(s,i,1);
        else
            addedge(i,t,1);
    }
    for(int i=1;i<=m;i++){  
        int a,b;
        scanf("%d %d",&a,&b);
        addedge(a,b,1);
        addedge(b,a,1);
    }
    printf("%d\n",dinic());
    return 0;
}

标签：善意,int,flow,vis,edges,MAXN,push,P2057,SHOI2007
来源： https://www.cnblogs.com/dreagonm/p/10500025.html