feat: 添加P3953.cpp实现最短路径计数功能

实现了一个基于Dijkstra算法的最短路径计数解决方案，用于计算在给定约束条件下从起点到终点的路径数量。包含输入处理、最短路径计算和路径计数逻辑。当路径步数超过阈值时返回-1，否则返回路径数模p的结果。

src/11/5/P3953.cpp

@@ -0,0 +1,93 @@
+#include <bitset>
+#include <cstdio>
+#include <deque>
+#include <iostream>
+#include <istream>
+#include <queue>
+#include <vector>
+using ll = int64_t;
+#define sl static inline
+// #define printf
+const ll maxm=2e5+5;
+ll n,m,k,p,nt;
+struct E{
+    ll v,w;
+};
+struct P{
+    ll now,step;
+    inline bool operator<(const P&o)const{
+        return step>o.step;
+    }
+};
+std::vector<std::vector<E>> edg;
+std::bitset<maxm> vis;
+std::deque<P>dq;
+
+sl ll dj(){
+    vis.reset();
+    std::priority_queue<P> pq;
+    pq.emplace(1,0);
+    while(pq.size()){
+        auto[now,step]=pq.top();
+        pq.pop();
+        if(now==n)return step;
+        if(vis[now])continue;
+        vis[now]=true;
+        for(auto[v,w]:edg[now]){
+            pq.emplace(v,step+w);
+        }
+    }
+    return -1;
+}
+
+sl void solve(){
+    printf("NT = %lld\n",++nt);
+    std::cin>>n>>m>>k>>p;
+    edg.clear();
+    edg.resize(n+1);
+    for(ll i=1;i<=m;i++){
+        ll u,v,w;
+        std::cin>>u>>v>>w;
+        edg[u].emplace_back(v,w);
+    }
+    const ll d = dj();
+    printf("found d=%lld\n",d);
+    if(d==-1){
+        std::cout<<"0\n";
+        return;
+    }
+    const ll ms=d+k;
+    ll ans=0;
+    dq.clear();
+    dq.emplace_back(1,0);
+    ll tick=0;
+    while(dq.size()){
+        tick++;
+        if(tick>1e6){
+            std::cout<<-1<<"\n";
+            return;
+        }
+        auto[now,step]=dq.front();
+        dq.pop_front();
+        if(now==n){
+            ans++;
+        }
+        for(auto[v,w]:edg[now]){
+            const ll ns=w+step;
+            if(ns>ms)continue;
+            dq.emplace_back(v,ns);
+        }
+    }
+    std::cout<<ans%p<<"\n";
+}
+
+int main(){
+    std::iostream::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    ll t;
+    std::cin>>t;
+    while(t--){
+        solve();
+    }
+}