P2939-[USACO09FEB]改造路Revamping Trails

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define _for(i,a,b) for(int i = (a);i < b;i ++)
 4 #define _rep(i,b) for(int i = (a);i > b;i --)
 5 #define INF 0x3f3f3f3f
 6 #define pb push_back
 7 #define maxn 5000039
 8 typedef long long ll;
 9 inline ll read()
10 {
11     ll ans = 0;
12     char ch = getchar(),last = ‘ ‘;
13     while(!isdigit(ch)) last = ch,ch = getchar();
14     while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - ‘0‘,ch = getchar();
15     if(last == ‘-‘) ans = -ans;
16     return ans;
17 }
18 inline void write(ll x)
19 {
20     if(x < 0) x = -x,putchar(‘-‘);
21     if(x >= 10) write(x / 10);
22     putchar(x % 10 + ‘0‘);
23 }
24 int n,m,k;
25 int tot,ver[maxn],Next[maxn],head[maxn],val[maxn];
26 void add(int x,int y,int t)
27 {
28     ver[++tot] = y,Next[tot] = head[x],head[x] = tot,val[tot] = t;
29 }
30 typedef pair<int,int> P;
31 int d[maxn];
32 void shortest_path(int s)
33 {
34     priority_queue<P,vector<P>,greater<P>> que;
35     memset(d,0x3f,sizeof(d));
36     d[s] = 0;
37     que.push(P{0,s});
38 
39     while(!que.empty())
40     {
41         P p = que.top();que.pop();
42         int v = p.second;
43         if(d[v] < p.first) continue;
44         for(int i = head[v]; i; i = Next[i])
45         {
46           //  cout << i << endl;
47             int y = ver[i];
48             int w = val[i];
49             if(d[y] > d[v] + w)
50             {
51                 d[y] = d[v] + w;
52                 que.push(P{d[y],y});
53             }
54         }
55     }
56 }
57 int main()
58 {
59     n = read(),m = read(),k = read();
60     _for(i,1,m+1)
61     {
62         int u,v,t;
63         u = read();v = read();t = read();
64         add(u,t),add(v,u,t);
65         _for(j,k+1)
66         {
67             add(j*n+u,j*n+v,add(j*n+v,j*n+u,t);
68             add((j-1)*n+u,0),add((j-1)*n+v,j*n+u,0);
69         }
70     }
71     shortest_path(1);
72     int ans = d[n];
73     _for(i,k+1)
74         ans = min(ans,d[i*n+n]);
75     write(ans);
76     return 0;
77 }