【费用流】NOI2008志愿者招募

#include<iostream>
#include<cstring>
#include<vector>
#include<queue>
#include<cstdio>
#include<algorithm>
using namespace std;

#define LL long long

inline int read(){
	int x=0,f=1;char c=getchar();
	for(;!isdigit(c);c=getchar()) if(c==‘-‘) f=-1;
	for(;isdigit(c);c=getchar()) x=x*10+c-‘0‘;
	return x*f;
}
const int INF=9999999;
const int MAXN=300000*3;

int N,M; 
int S,T;
int Root[MAXN+1],Node[MAXN+1],Next[MAXN+1],Cost[MAXN+1],C[MAXN+1];
int dis[MAXN+1]; bool inq[MAXN+1];
int cnt;

void insert(int u,int v,int w,int c){
	Node[cnt]=v; Cost[cnt]=c; 
	C[cnt]=w; Next[cnt]=Root[u];
	Root[u]=cnt; ++cnt; return ;
}
bool BFS(){
	memset(inq,false,sizeof(inq));
	for(int i=0;i<=N;i++) dis[i]=INF;
	dis[T]=0; inq[T]=true;
	deque<int> Que; Que.push_front(T);
	while(!Que.empty()){
		int k=Que.front(); Que.pop_front();
		for(int x=Root[k];x>-1;x=Next[x]){
			int v=Node[x];
			if(C[x^1]>0&&dis[v]>dis[k]-Cost[x]){
				dis[v]=dis[k]-Cost[x];
				if(!inq[v]){
					inq[v]=true;
					if(!Que.empty()&&dis[Que.front()]>=dis[v]) Que.push_front(v);
					else Que.push_back(v);
				}
			}
		}
		inq[k]=false;
	}
	return dis[S]<INF;
}
int ans=0;
int DFS(int k,int t){
	if(k==T){inq[T]=1;return t;}
	int res=0; inq[k]=1;
	for(int x=Root[k];x>-1;x=Next[x]){
		int v=Node[x];
		if(C[x]>0&&!inq[v]&&dis[v]==dis[k]-Cost[x]){
			int tmp=DFS(v,min(C[x],t));
			if(!tmp) continue;
			t-=tmp; ans+=tmp*Cost[x]; C[x]-=tmp; C[x^1]+=tmp;
			res+=tmp;
			if(!t) return res;
		}
	}
	return res;
}

int main(){
    N=read(),M=read();
    for(int i=0;i<MAXN;i++) Root[i]=-1;
	S=2*N+1,T=2*N+2;
	for(int i=1;i<=N;i++){
		int t=read();
		insert(i,i+N,INF,0);
		insert(i+N,i,0,0);
		insert(S,i+N,t,0);
		insert(i+N,S,0,0);
		insert(i,T,t,0);
		insert(T,i,0,0);
	}
	for(int i=1;i<N;i++)
		insert(i+N,i+1,INF,0),insert(i+1,i+N,0,0);
	for(int i=1;i<=M;i++){
		int u=read(),v=read(),c=read();
		insert(v+N,u,INF,c);
		insert(u,v+N,0,-c);
	}
	N=N*2+2;
	--cnt;
	while(BFS()) {
		DFS(S,INF);
	}
	printf("%d\n",ans);
	return 0;
}