51nod 1442 士兵的旅行

#include <bits/stdc++.h>

using namespace std;

const int maxn = 105*2;
const int INF = 0x3f3f3f3f;

struct Edge {
int from,to,cap,flow;
};

struct Dinic
{
int n,m,s,t;
vector<Edge> edge;
vector<int> G[maxn];
bool vis[maxn];
int d[maxn];
int cur[maxn];

void init()
{
for(int i=0;i<maxn;i++)
G[i].clear();
edge.clear();
memset(d,0,sizeof(d));
memset(vis,0,sizeof(vis));
memset(cur,0,sizeof(cur));
}

void addEdge (int from,int to,int cap)
{
edge.push_back((Edge){from,to,cap,0});
edge.push_back((Edge){to,from,0,0});
m = edge.size();
G[from].push_back(m-2);
G[to].push_back(m-1);
}

bool BFS()
{
memset(vis,0,sizeof(vis));
queue<int> Q;
Q.push(s);
d[s] = 0;
vis[s] = 1;
while(!Q.empty())
{
int x = Q.front();
Q.pop();
for(int i=0; i<G[x].size(); i++)
{
Edge & e = edge[G[x][i]];
if(!vis[e.to]&&e.cap>e.flow)
{
vis[e.to] = 1;
d[e.to] = d[x] + 1;
Q.push(e.to);
}
}
}
return vis[t];
}

int DFS(int x,int a)
{
if(x==t||a==0) return a;
int flow = 0,f;
for(int & i = cur[x]; i<G[x].size(); i++)
{
Edge & e = edge[G[x][i]];
if(d[x] + 1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
{
e.flow +=f;
edge[G[x][i]^1].flow -=f;
flow +=f;
a-=f;
if(a==0) break;
}
}
return flow;
}

int Maxflow (int s,int t) {
this->s = s;this->t = t;
int flow = 0;
while(BFS()) {
memset(cur,0,sizeof(cur));
flow+=DFS(s,INF);
}
return flow;
}

}sol;

int main()
{
int n,m;
scanf("%d%d",&n,&m);

int s = 0;
int t = 2*n+1;

sol.init();
int sum = 0;
for(int i=1;i<=n;i++) {
int a;
scanf("%d",&a);
sum +=a;
sol.addEdge(s,i,a);
sol.addEdge(i,i+n,INF);
}

int sum2 = 0;
for(int i=1;i<=n;i++) {
int a;
scanf("%d",&a);
sum2+=a;
sol.addEdge(i+n,t,a);
}

for(int i=0;i<m;i++) {
int u,v;
scanf("%d%d",&u,&v);
sol.addEdge(u,v+n,INF);
sol.addEdge(v,u+n,INF);
}

int ans = sol.Maxflow(s,t);
if(ans==sum&&sum2==sum)
puts("YES");
else puts("NO");

return 0;
}