Luogu 4822

题目分析 ：

• 注意边界：

for(int i=0;i<=k;++i) f[s][i]=0

Code:

#include <bits/stdc++.h>
using namespace std;
#define maxn 60
#define maxm 1010
#define maxk 55
#define INF 9187201950435737471

int n,m,k,s,t,head[maxn],size=0;
long long f[maxn][maxk];
bool vis[maxn][maxk];
struct edge {
	int v,nxt,w;
}e[maxm<<1];
struct hepnode {
	int pos,AKIOI;
	long long dis;
	bool operator < (const hepnode& rhs) const {
		return dis > rhs.dis;
	}  
};

inline 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-'0';
		c=getchar();
	}
	return x*f;
}

inline void clean_() {
	memset(head,-1,sizeof(head));
	memset(f,0x7f,sizeof(f));
	memset(vis,false,sizeof(vis));
}

inline void add_(int u,int v,int w) {
	e[++size].v=v;
	e[size].w=w;
	e[size].nxt=head[u];
	head[u]=size;
}

inline void Dijkstra_() {
	for(int i=0;i<=k;++i) {
		f[s][i]=0;
	}
	priority_queue<hepnode>q;
	q.push( (hepnode) {s,0,f[s][0]} );
	vis[s][0]=true;
	while(!q.empty()) {
		hepnode pdc=q.top();
		q.pop();
		int u=pdc.pos,AKNOI=pdc.AKIOI;
		vis[u][AKNOI]=false;
		for(int i=head[u];~i;i=e[i].nxt) {
			int v=e[i].v,w=e[i].w;
			if(f[v][0]==INF||f[v][0]>f[u][0]+w) {
				f[v][0]=f[u][0]+w;
				if(!vis[v][0]) {
					vis[v][0]=true;
					q.push( (hepnode) {v,0,f[v][0]} );
				}		
			}  
			for(int j=1;j<=k;++j) {
				if(f[v][j]>min(f[u][j-1]+(w/2),f[u][j]+w)) {
					f[v][j]=min(f[u][j-1]+(w/2),f[u][j]+w);
					if(!vis[v][j]) {
						vis[v][j]=true;
						q.push( (hepnode) {v,j,f[v][j]} );
					}
				} 
			}
		}
 	}
 	printf("%lld",f[t][k]);
 	//A了2939,再A了4568，还要A了4822
}

void readda_() {
	n=read_();m=read_();k=read_();
	s=1;t=n;
	clean_();
	int x,y,z;
	for(int i=1;i<=m;++i) {
		x=read_();y=read_();z=read_();
		add_(x,y,z);add_(y,x,z);
	}
	Dijkstra_();
}

int main() {
	freopen("a.txt","r",stdin);
	readda_();
	return 0;
}