P3275 [SCOI2011]糖果

 

 

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调了好久的差分约束，话说倒序加边真的玄学

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#include<bits/stdc++.h>
using namespace std;
const int bow=100010;
int n,m,a,b,c,ne,head[bow],vist[bow],usd[bow<<2],d[bow];
struct node{int nxt,to,dis;}eg[bow<<2];
void adde(int u,int v,int val){eg[++ne].nxt=head[u];eg[ne].to=v;eg[ne].dis=val;head[u]=ne;}
int spfa(){
    queue<int>q;
    q.push(0);d[0]=0;vist[0]=1;
    while(!q.empty()){
    int u=q.front();
    q.pop();vist[u]=0;
    for(int i=head[u];i;i=eg[i].nxt)
        if(d[eg[i].to]<d[u]+eg[i].dis){
            d[eg[i].to]=d[u]+eg[i].dis;usd[i]++;if(usd[i]>n-1)return 0;
            if(!vist[eg[i].to]){vist[eg[i].to]=1;q.push(eg[i].to);}
        }  
    }
   return 1;
}
int main()
{
    cin>>n>>m;
    int flg=0;
    while(m--)
    {
        scanf("%d%d%d",&c,&a,&b);
        if(c==1){adde(a,b,0);adde(b,a,0);}
        if(c==2)adde(a,b,1);
        if(c==3)adde(b,a,0);
        if(c==4)adde(b,a,1);
        if(c==5)adde(a,b,0);
        if(c%2==0&&a==b)flg=1;
    }
    if(flg==1){cout<<-1;return 0;}
    for(int i=n;i>=1;i--)adde(0,i,1);
    if(!spfa())cout<<-1;
    else{
        long long ans=0;
        for(int i=1;i<=n;i++)ans+=d[i];
        cout<<ans;
    }
    
}