bzoj1061 志愿者招募

传送门

分析

https://www.luogu.org/problemnew/solution/P3980

代码

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdlib>
#include<queue>
#include<ctime>
#include<vector>
#include<set>
#include<map>
#include<stack>
#include<climits>
using namespace std;
const int inf = INT_MAX;
int n,m,f[40010],mf[40010],pre[40010],from[40010];
int head[40010],nxt[40010],to[40010];
int cost[40010],ath[40010],fr[40010],cnt;
int d[40010];
bool iq[40010];
int s,t,Ans;
int q[400100],fi,la;
inline void add(int x,int y,int z,int c){
    nxt[++cnt]=head[x];
    head[x]=cnt;
    to[cnt]=y;
    f[cnt]=z;
    cost[cnt]=c;
    fr[cnt]=x;
    nxt[++cnt]=head[y];
    head[y]=cnt;
    to[cnt]=x;
    f[cnt]=0;
    cost[cnt]=-c;
    fr[cnt]=y;
    ath[cnt]=cnt-1;ath[cnt-1]=cnt;
}
inline void go(){
    register int i;
    while(1){
      for(i=s;i<=t;i+=4)d[i]=d[i+1]=d[i+2]=d[i+3]=inf;
      fi=la=100001;
      q[fi]=s;
      d[s]=0;
      iq[s]=1;
      int flow=inf;
      while(fi<=la){
          int x=q[fi];
        fi++;
        iq[x]=0;
        if(d[x]>=inf)continue;
        for(i=head[x];i;i=nxt[i]){
          if(f[i]&&d[to[i]]>d[x]+cost[i]){
              d[to[i]]=d[x]+cost[i];
              pre[to[i]]=i;
              flow=min(flow,f[i]);
              if(!iq[to[i]]){
                if(d[to[i]]>d[q[fi]])q[++la]=to[i];
                  else q[--fi]=to[i];
                iq[to[i]]=1;
              }
          }
        } 
      }
      if(d[t]>=inf)return;
      int wh=pre[t];
      while(wh){
          f[wh]-=flow;
          f[ath[wh]]+=flow;
          Ans+=flow*cost[wh];
          wh=pre[fr[wh]];
      }
    }
}
inline int ra(){
    int x=0,f=1;char s=getchar();
    while(!isdigit(s)){if(s=='-')f=-1;s=getchar();}
    while(isdigit(s))x=(x<<3)+(x<<1)+(s-'0'),s=getchar();
    return x*f;
}
int main(){
    register int i;
    n=ra(),m=ra();
    s=0,t=n+2;
    for(i=1;i<=n;++i){
      int x;
      x=ra();
      add(i,i+1,inf-x,0);
    }
    add(s,1,inf,0),add(n+1,n+2,inf,0);
    for(i=1;i<=m;++i){
      int x,y,z;
      x=ra(),y=ra(),z=ra();
      add(x,y+1,inf,z);
    }
    go();
    printf("%d\n",Ans);
    return 0;
}