Luogu3953 NOIP2017逛公园（最短路+拓扑排序+动态规划）

　　跑一遍dij根据最短路DAG进行拓扑排序，按拓扑序dp即可。wa了三发感觉非常凉。

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<queue>
using namespace std;
#define ll long long
#define N 100010
#define M 200010 
#define K 51
char getc(){char c=getchar();while ((c<'A'||c>'Z')&&(c<'a'||c>'z')&&(c<'0'||c>'9')) c=getchar();return c;}
int gcd(int n,int m){return m==0?n:gcd(m,n%m);}
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
int T,n,m,k,P,p[N],d[N],from[M],f[N][K],Q[N],degree[N],t;
bool flag[N];
struct data{int to,nxt,len;
}edge[M];
struct data2
{
    int x,d;
    bool operator <(const data2&a) const
    {
        return d>a.d;
    }
};
priority_queue<data2> q;
void inc(int &x,int y){x+=y;if (x>=P) x-=P;}
void addedge(int x,int y,int z){t++;edge[t].to=y,edge[t].nxt=p[x],edge[t].len=z;p[x]=t;}
void dijkstra()
{
    memset(d,42,sizeof(d));d[1]=0;
    memset(flag,0,sizeof(flag));
    q.push((data2){1,0});
    for (;;)
    {
        while (!q.empty()&&flag[q.top().x]) q.pop();
        if (q.empty()) break;
        data2 x=q.top();q.pop();flag[x.x]=1;
        for (int i=p[x.x];i;i=edge[i].nxt)
        if (x.d+edge[i].len<d[edge[i].to])
        {
            d[edge[i].to]=x.d+edge[i].len;
            q.push((data2){edge[i].to,d[edge[i].to]});
        }
    }
}
bool topsort()
{
    memset(degree,0,sizeof(degree));
    for (int i=1;i<=m;i++) 
    if (d[from[i]]+edge[i].len==d[edge[i].to]) degree[edge[i].to]++;
    int head=0,tail=0;for (int i=1;i<=n;i++) if (!degree[i]) Q[++tail]=i;
    while (head<tail&&tail<n)
    {
        int x=Q[++head];
        for (int i=p[x];i;i=edge[i].nxt)
        if (d[x]+edge[i].len==d[edge[i].to])
        {
            degree[edge[i].to]--;
            if (!degree[edge[i].to]) Q[++tail]=edge[i].to;
        }
    }
    return tail<n;
}
int main()
{
    T=read();
    while (T--)
    {
        n=read(),m=read(),k=read(),P=read();
        t=0;memset(p,0,sizeof(p));
        for (int i=1;i<=m;i++)
        {
            int x=read(),y=read(),z=read();
            from[i]=x;addedge(x,y,z);
        }
        dijkstra();
        if (topsort()) cout<<-1<<endl;
        else
        {
            memset(f,0,sizeof(f));f[1][0]=1;
            for (int i=0;i<=k;i++)
                for (int j=1;j<=n;j++)
                {
                    int x=Q[j];
                    for (int y=p[x];y;y=edge[y].nxt)
                    {
                        int u=d[x]+edge[y].len-d[edge[y].to]+i;
                        if (u<=k) inc(f[edge[y].to][u],f[x][i]);
                    }
                }
            int ans=0;
            for (int i=0;i<=k;i++) inc(ans,f[n][i]);
            cout<<ans<<endl;
        }
    }
    return 0;
}