BZOJ1061: [Noi2008]志愿者招募

#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 1005
#define maxm 10005
using namespace std;
const int inf=0x7fffffff;
int ans,n,m,tot,s,t,h[maxn],way[maxm*4],next[maxm*4],ww[maxm*4],cap[maxm*4],a[maxn],pre[maxn];
int read(){
  int x=0,f=1;char ch;
  for(ch=getchar();ch<‘0‘||ch>‘9‘;ch=getchar())if(ch==‘-‘)f=-1;
  for(;ch>=‘0‘&&ch<=‘9‘;ch=getchar())x=x*10+ch-‘0‘;
  return x*f;
}
void add(int x,int y,int w,int c){way[++tot]=y;next[tot]=h[x];h[x]=tot;ww[tot]=w;cap[tot]=c;}
void insert(int x,int y,int w,int c=inf){add(x,y,w,c);add(y,x,-w,0);}
int head,tail,d[maxn+10],dist[maxn];
bool v[maxn];
bool spfa(){
  memset(v,0,sizeof(v));v[s]=1;pre[s]=-1;
  for(int i=0;i<=t;i++)dist[i]=inf;dist[s]=0;
  head=0;tail=1;d[0]=s;
  while(head!=tail){
    int x=d[head];head++;if(head>maxn)head=0;
    for(int j=h[x];j;j=next[j])if(cap[j]&&dist[way[j]]>dist[x]+ww[j]){
    dist[way[j]]=dist[x]+ww[j];pre[way[j]]=j;
    if(!v[way[j]]){
      v[way[j]]=1;d[tail++]=way[j];if(tail>maxn)tail=0;
    }
      }
    v[x]=0;
  }
  return dist[t]!=inf;
}
int find(){
  int delt=inf,x=0;
  for(int j=t;j!=s;j=way[pre[j]^1]){
    delt=min(delt,cap[pre[j]]);
  }
  for(int j=t;j!=s;j=way[pre[j]^1]){
    x=x+delt*ww[pre[j]];cap[pre[j]]-=delt;cap[pre[j]^1]+=delt;
  }
  return x;
}
int main(){
  n=read();m=read();tot=1;
  for(int i=1;i<=n;i++)a[i]=read();
  for(int i=1,x,y,z;i<=m;i++){
    x=read();y=read();z=read();
    insert(x,y+1,z);
  }
  s=0;t=n+2;
  for(int i=1;i<=n+1;i++){
    int x=a[i]-a[i-1];
    if(x>=0)insert(s,i,0,x);
    else insert(i,t,0,-x);
    if(i>1)insert(i,i-1,0);
  }
  while(spfa())ans+=find();
  printf("%d\n",ans);
  return 0;
}