luogu P2740 [USACO4.2]草地排水Drainage Ditches

题面传送门
直接上\(dicnic\)板子即可，注意加几个剪枝，跑得飞快。
代码实现:

#include<cstdio>
#include<cstring>
#include<queue>
#define min(a,b) ((a)<(b)?(a):(b))
using namespace std;
int n,m,k,x,y,z,d[1039],now[1039],st,t,nows,cur;
long long ans;
struct yyy{int to,w,z;}tmp;
struct ljb{
	int head,h[1039];
	yyy f[10039];
	inline void add(int x,int y,int z){
		f[head]=(yyy){y,z,h[x]};
		h[x]=head++;
	}
}s;
queue<int > q;
inline int bfs(){
	while(!q.empty()) q.pop();
	memset(d,0x3f,sizeof(d));
	q.push(st);
	d[st]=0;
	now[st]=s.h[st];
	while(!q.empty()){
		nows=q.front();
		q.pop();
		cur=s.h[nows];
		while(cur!=-1){
			tmp=s.f[cur];
			if(tmp.w&&d[tmp.to]>=1e9) {
				d[tmp.to]=d[nows]+1;now[tmp.to]=s.h[tmp.to];q.push(tmp.to);
				if(tmp.to==t) return 1;
			}
			cur=tmp.z;
		}
	}
	return 0;
}
inline long long dfs(int x,long long sum){
	if(x==t) return sum;
	long long k,pus=0;
	int cur=now[x];
	yyy tmp;
	while(cur!=-1){
		tmp=s.f[cur];
		now[x]=cur;
		if(d[tmp.to]==d[x]+1&&tmp.w){
			k=dfs(tmp.to,min(tmp.w,sum));
			if(!k) d[tmp.to]=1e9;
			s.f[cur].w-=k;
			s.f[cur^1].w+=k;
			pus+=k;
			sum-=k;
		}
		if(!sum) break;
		cur=tmp.z;
	}
	return pus;
}
int main(){
	//freopen("1.in","r",stdin);
	register int i;
	memset(s.h,-1,sizeof(s.h));
	scanf("%d%d",&m,&n);
	st=1;t=n;
	for(i=1;i<=m;i++) scanf("%d%d%d",&x,&y,&z),s.add(x,y,z),s.add(y,x,0);
	while(bfs())ans+=dfs(st,1e15);
	printf("%lld\n",ans);
}