[BZOJ 1579] Revamping Trails

[题目链接]

         https://www.lydsy.com/JudgeOnline/problem.php?id=1579

[算法]

        dist[u][k]表示当前在点u，升级了k条道路，最短路径的长度

        dijkstra即可

[代码]

        

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100010
#define MAXM 50010
#define MAXK 25

int i,n,m,k,u,v,w,tot;
int dist[MAXN][MAXK];
int head[MAXN];

struct edge
{
        int to,w,nxt;
} e[MAXM << 1];
inline void addedge(int u,int v,int w)
{
        tot++;
        e[tot] = (edge){v,w,head[u]};
        head[u] = tot;
}
inline void dijkstra()
{
        int i,v,w;
        static bool visited[MAXN][MAXK];
        pair<int,int> cur;
        priority_queue< pair<int,pair<int,int> > > q;
        memset(visited,false,sizeof(visited));
        memset(dist,0x3f,sizeof(dist));
        dist[1][0] = 0;
        q.push(make_pair(0,make_pair(1,0)));
        while (!q.empty())
        {
                cur = q.top().second;
                q.pop();
                if (visited[cur.first][cur.second]) continue;
                visited[cur.first][cur.second] = true;
                for (i = head[cur.first]; i; i = e[i].nxt)
                {
                        v = e[i].to;
                        w = e[i].w;
                        if (dist[cur.first][cur.second] + w < dist[v][cur.second])
                        {
                                dist[v][cur.second] = dist[cur.first][cur.second] + w;
                                q.push(make_pair(-dist[v][cur.second],make_pair(v,cur.second))); 
                        }
                        if (cur.second < k && dist[cur.first][cur.second] < dist[v][cur.second + 1]) 
                        {
                                dist[v][cur.second + 1] = dist[cur.first][cur.second];
                                q.push(make_pair(-dist[v][cur.second + 1],make_pair(v,cur.second + 1)));
                        }
                }
        }
}
int main() 
{
        
        scanf("%d%d%d",&n,&m,&k);
        for (i = 1; i <= m; i++)
        {
                scanf("%d%d%d",&u,&v,&w);
                addedge(u,v,w);
                addedge(v,u,w);
        }
        dijkstra();
        printf("%d\n",dist[n][k]);
        
        return 0;
    
}