NEFU 655 Trip（DP）

Trip

Time Limit 1000ms Memory Limit 65536K

description

Xiao wang has a new car, so he wants to have a trip from his home to hefei, however, there is no road from his house directly to Hefei, so he has to go through a number of cities to get to hefei, his car takes one unit of time driving a unit distance at first, but his car will be slow after every city that he pass, so he will take one more unit of time to take a unit of distance after every city (that is, if he has passed k cities, then he needs k units of time to take a unit of distance, we think his home is the first city), can you tell him how to spend the least time to reach Hefei?

input

The first line contains two numbers n and m (0 < n ≤ 200, 0 < m < n×(n-1)/2 ), n is the number of city, 1 is xiaowang's home, n is hefei, m is the number of road, bi-directional edge, then the following m line contains 3 numbers x, y, z, means there is a road from x to y, the distance is z.(You can make sure that there is always a path exist between his home ande hefei).

output

The least time xiao wang must use from his home to hefei.

sample_input

5 6 1 2 1 1 4 5 2 3 2 3 5 1 4 5 1 2 4 2

sample_output

7

hint

source

思路：dp[x][y]从起始点能经过y个城市到达x城市的最优值

g[a][b]为城市a到城市b的距离

dp[x][y]=min(dp[k][y-1]+y*g[k][x])

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
const int mm=210;
const long long oo=1e18;
long long g[mm][mm];
long long dp[mm][mm];
int n,m;
int main()
{ int a,b,c;
  while(cin>>n>>m)
  { memset(g,-1,sizeof(g));
      for(int i=0;i<=n;++i)
      for(int j=0;j<=n;++j)
      dp[i][j]=oo;
    for(int i=0;i<m;++i)
    {scanf("%d%d%d",&a,&b,&c);
     g[a][b]=g[b][a]=c;
    }
    dp[1][0]=0;
    for(int i=1;i<=n;++i)
    {
      for(int j=1;j<=n;++j)
      {
        for(long long k=1;k<=n;++k)
          if(g[i][j]!=-1)
        dp[j][k]=min(dp[j][k],dp[i][k-1]+k*g[i][j]);
      }
    }
    long long ans=oo;
    for(int i=1;i<=n;++i)
      ans=min(ans,dp[n][i]);
      cout<<ans<<"\n";
  }
}