题目
某人至少要花多少钱才能到达学校。
分析
spfa后,听取WA声一片,所以看了解题报告后发现是dp
(而且比深搜慢)
状态转移方程:
dp代码
#include <cstdio>
#include <cctype>
#include <cstring>
using namespace std;
int n,t,m,x[51],y[51],l[51],r[51],w[51],f[100001][51];
int in(){
int ans=0; char c=getchar();
while (!isdigit(c)) c=getchar();
while (isdigit(c)) ans=ans*10+c-48,c=getchar();
return ans;
}
int main(){
freopen("shaxu.in","r",stdin);
freopen("shaxu.out","w",stdout);
n=in(); t=in(); m=in(); memset(f,127/3,sizeof(f)); f[0][1]=0;
for (int i=1;i<=m;i++) x[i]=1+in(),y[i]=1+in(),l[i]=in(),r[i]=l[i]+1+in(),w[i]=in();
for (int i=0;i<=t;i++)
for (int j=1;j<=n;j++){
if (f[i][j]==707406378) continue;
for (int k=1;k<=m;k++)
if (x[k]==j&&l[k]==i&&r[k]<=t+1)
if (f[i][j]+w[k]<f[r[k]][y[k]]) f[r[k]][y[k]]=f[i][j]+w[k];
if (f[i+1][j]>f[i][j]) f[i+1][j]=f[i][j];
}
if (f[t+1][n]==707406378) return !puts("-1"); else return !printf("%d",f[t+1][n]);
}
深搜代码
#include <cstdio>
#include <cctype>
#include <algorithm>
using namespace std;
unsigned short n,m,ls[51]; int mint=2147483647,t; bool v[51];
struct node{int x,y,must,last,w,next;}e[51];
int in(){
int ans=0; char c=getchar();
while (!isdigit(c)) c=getchar();
while (isdigit(c)) ans=ans*10+c-48,c=getchar();
return ans;
}
void dfs(int x,int cost,int now){
if (x==n&&now<=t) {mint=min(mint,cost); return;}
v[x]=1; int p=ls[x];
while (p){
if (!v[e[p].y]&&now<e[p].must)
dfs(e[p].y,cost+e[p].w,e[p].must+e[p].last);
p=e[p].next;
}
v[x]=0;
}
int main(){
freopen("shaxu.in","r",stdin);
freopen("shaxu.out","w",stdout);
n=in(); t=in(); m=in();
for (int i=1;i<=m;i++){
e[i].x=in()+1; e[i].y=in()+1; e[i].must=in(); e[i].last=in();
e[i].w=in(); e[i].next=ls[e[i].x]; ls[e[i].x]=i;
if (e[i].x==1&&e[i].must==0) e[i].must++;
}
dfs(1,0,0);
if (mint==2147483647) return !puts("-1");
return !printf("%d",mint);
}