【分层图最短路，dijstra】P2939 [USACO09FEB]改造路Revamping Trails

  1 #include<iostream>
  2 #include<string>
  3 #include<queue>
  4 #include<stack>
  5 #include<vector>
  6 #include<map>
  7 #include<cstdio>
  8 #include<cstdlib>
  9 #include<algorithm>
 10 #include<set>
 11 #include<list>
 12 #include<iomanip>
 13 #include<cstring>
 14 #include<cmath>
 15 #include<limits>
 16 using namespace std;
 17 
 18 #define au auto
 19 #define debug(i) cout<<"<debug> "<<i<<"<\debug>"<<endl
 20 #define mfor(i,a,b) for(register int i=(a);i<=(b);i++)
 21 #define mrep(i,a,b) for(register int i=(a);i>=(b);i--)
 22 #define LLL __int128
 23 #define Re register
 24 #define il inline
 25 #define mem(a,b) memset(a,(b),sizeof(a))
 26 typedef pair<int, int> intpair;
 27 typedef long long int LL;
 28 const int INF = 0x3f3f3f3f;
 29 const long long int INFLL = 0x3f3f3f3f3f3f3f3f;
 30 
 31 int cnt;
 32 const int maxn = 5000010;
 33 int n, m, k;
 34 
 35 struct Edge
 36 {
 37     int u, nxt;
 38     int w;
 39 }e[maxn];
 40 
 41 int head[maxn];
 42 
 43 void add(int a, int b, int w)
 44 {
 45     e[++cnt].u = b;
 46     e[cnt].nxt = head[a];
 47     head[a] = cnt;
 48     e[cnt].w = w;
 49 }
 50 
 51 typedef struct
 52 {
 53     bool operator ()(const intpair& a, const intpair& b)const
 54     {
 55         return a.second > b.second;
 56     }
 57 }cmp;
 58 
 59 int dis[maxn];
 60 bool vis[maxn];
 61 priority_queue<intpair, vector<intpair>, cmp>q;
 62 
 63 void dijstra(int x)
 64 {
 65     mem(dis, 0x3f);
 66     mem(vis, false);
 67     dis[x] = 0;
 68     q.push(intpair(x, dis[x]));
 69     while (!q.empty())
 70     {
 71         intpair t = q.top();
 72         q.pop();
 73         if (vis[t.first]) continue;
 74         vis[t.first] = true;
 75         for (int i = head[t.first]; i != -1; i = e[i].nxt)
 76         {
 77             int u = e[i].u;
 78             int w = e[i].w;
 79             if (!vis[u] && dis[u] > t.second + w)
 80             {
 81                 dis[u] = t.second + w;
 82                 q.push(intpair(u, dis[u]));
 83             }
 84         }
 85     }
 86 }
 87 
 88 int main()
 89 {
 90     cin >> n >> m >> k;
 91     mem(head, -1);
 92     mfor(i, 1, m)
 93     {
 94         int a, b, c;
 95         cin >> a >> b >> c;
 96         add(a, b, c);
 97         add(b, a, c);
 98         mfor(j, 1, k)
 99         {
100             add(j * n + a, j * n + b, c);
101             add(j * n + b, j * n + a, c);
102             add((j - 1) * n + a, j * n + b, 0);
103             add((j - 1) * n + b, j * n + a, 0);
104         }
105     }
106     dijstra(1);
107     int ans = dis[n];
108     mfor(i, 1, k)
109     {
110         ans = min(ans, dis[i * n + n]);
111     }
112     cout << ans;
113     return 0;
114 }

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