到底是哪里写挂了

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int N=20010;
const int inf=1e18;
int T,n,m,a[50][50],s,t;
int cb,cw,sb,sw,mx,ans;
struct node{int to,nxt,w;}e[N<<1];
int head[N],cnt=1,now[N],dis[N],sum;
const int dx[]={0,0,-1,1};
const int dy[]={-1,1,0,0};
void add(int u,int v,int w)
{
    e[++cnt]={v,head[u],w};head[u]=cnt;
    e[++cnt]={u,head[v],0};head[v]=cnt;
}
bool bfs()
{
    for(int i=1;i<=t;i++) now[i]=head[i],dis[i]=inf;
    queue<int>q;q.push(s);
    dis[s]=0;
    while(!q.empty())
    {
        int x=q.front();
        q.pop();
        for(int i=head[x];i;i=e[i].nxt)
        {
            int y=e[i].to;
            if(e[i].w&&dis[y]==inf)
            {
                dis[y]=dis[x]+1;
                q.push(y);
            }
        }
    }
    return dis[t]!=inf;
}
int dfs(int x,int flow)
{
    int res=0;
    if(x==t) return flow;
    for(int i=now[x];i&&flow;i=e[i].nxt)
    {
        now[x]=i;
        int y=e[i].to;
        if(!e[i].w||dis[y]!=dis[x]+1) continue;
        int k=dfs(y,min(e[i].w,flow));
        e[i].w-=k,e[i^1].w+=k,res+=k,flow-=k;
    }
    return res;
}
int dinic()
{
    int res=0;
    while(bfs()) res+=dfs(s,inf);
    return res;
}
bool check(int x)
{
    sum=0,cnt=1;//memset(e,0,sizeof(e));
    memset(head,0,sizeof(head));
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if((i+j)%2==0) 
            {
                sum+=x-a[i][j];
                add(s,i*40+j,x-a[i][j]);
                //cout<<s<<" "<<i*40+j<<endl;
                for(int k=0;k<4;k++)
                {
                    int xx=i+dx[k],yy=j+dy[k];
                    add(i*40+j,xx*40+yy,inf);
                    //cout<<i*40+j<<" "<<xx*40+yy<<endl;
                }
            }
            else add(i*40+j,t,x-a[i][j]);//cout<<i*40+j<<" "<<t<<endl;
        }
    }
    return dinic()==sum;
}
signed main()
{
    //freopen("code.out","w",stdout);
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    cin>>T;
    while(T--)
    {
        cin>>n>>m;s=n*40+m+1,t=n*40+m+2;
        cw=cb=sw=sb=mx=0;
        for(int i=1;i<=n;i++)
        {
            for(int j=1;j<=m;j++)
            {
                cin>>a[i][j];mx=max(a[i][j],mx);
                if((i+j)%2==0) cb++,sb+=a[i][j];
                else cw++,sw+=a[i][j];
            }
        }
        if(cb!=cw)
        {
            int x=(sb-sw)/(cb-cw);
            if(x>=mx&&check(x)){cout<<cb*x-sb<<"\n";}
            else cout<<"-1\n";
        }
        else
        {
            if(sb!=sw) cout<<"-1\n";
            else
            {
                int l=mx,r=inf;ans=-1;
                while(l<=r)
                {
                    int mid=(l+r)>>1;
                    if(check(mid)) r=mid-1,ans=mid;
                    else l=mid+1;
                }
                if(ans==-1)cout<<"-1\n";
                else cout<<ans*cb-sb<<"\n";
            }
        }
    }
    return 0;
}