POJ 1716 差分約束 SPFA

和上題一樣的解法。代碼也一樣，一樣糾結了很久。一樣不知道為什麼！！

#include<iostream>#include<queue>#define MAXN 20001#define INF 0x7F7F7F7Fusing namespace std;struct Node{       int v,price;       Node *next;}Edge[MAXN<<2],*ptr[MAXN];int N;int minV,maxV;int EdgeNum;void addEdge( int u,int v,int w ){     Node *p=&Edge[EdgeNum++];     p->v=v;     p->price=w;     p->next=ptr[u];     ptr[u]=p;}int dist[MAXN];void spfa( ){     bool used[MAXN];     queue<int>myQueue;     while( !myQueue.empty() ) myQueue.pop();          memset( used,0,sizeof(used) );     memset( dist,0xFF,sizeof(dist) );     dist[minV]=0;     myQueue.push(minV);     while( !myQueue.empty() )     {            int u=myQueue.front();            myQueue.pop();            Node *p=ptr[u];            used[u]=false;            while( p )            {                   if( dist[p->v]<dist[u]+p->price )                   {                       dist[p->v]=dist[u]+p->price;                       if( !used[p->v] )                       {                           used[p->v]=true;                           myQueue.push(p->v);                       }                   }                   p=p->next;             }     }     return ;} int main(){        while( scanf( "%d",&N )!=EOF )    {           int i,j;           int a,b;           EdgeNum=0;           maxV=0;minV=INF;           for( i=0;i<=N;i++ )                ptr[i]=NULL;           for( i=1;i<=N;i++ )           {                scanf( "%d %d",&a,&b );                if( minV>a )minV=a;                if( maxV<b+1 )maxV=b+1;                addEdge( a,b+1,2 );           }           for( i=minV;i<=maxV;i++ )           {                addEdge( i,i+1,0 );                addEdge( i+1,i,-1 );           }           spfa();           printf( "%d\n",dist[maxV] );    }    return 0;   }