hdu 2923 Floyd

本文介绍了一种利用Floyd算法解决城市中回收破车最优路径的问题,通过将字符串映射为数字并考虑单向与双向道路的影响,实现了计算从公司车库出发回收所有破车所需的最短总距离。

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题目:

Einbahnstrasse

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3405    Accepted Submission(s): 1074


Problem Description
Einbahnstra  e (German for a one-way street) is a street on which vehicles should only move in one direction. One reason for having one-way streets is to facilitate a smoother flow of traffic through crowded areas. This is useful in city centers, especially old cities like Cairo and Damascus. Careful planning guarantees that you can get to any location starting from any point. Nevertheless, drivers must carefully plan their route in order to avoid prolonging their trip due to one-way streets. Experienced drivers know that there are multiple paths to travel between any two locations. Not only that, there might be multiple roads between the same two locations. Knowing the shortest way between any two locations is a must! This is even more important when driving vehicles that are hard to maneuver (garbage trucks, towing trucks, etc.)

You just started a new job at a car-towing company. The company has a number of towing trucks parked at the company's garage. A tow-truck lifts the front or back wheels of a broken car in order to pull it straight back to the company's garage. You receive calls from various parts of the city about broken cars that need to be towed. The cars have to be towed in the same order as you receive the calls. Your job is to advise the tow-truck drivers regarding the shortest way in order to collect all broken cars back in to the company's garage. At the end of the day, you have to report to the management the total distance traveled by the trucks.
 

Input
Your program will be tested on one or more test cases. The first line of each test case specifies three numbers (N , C , and R ) separated by one or more spaces. The city has N locations with distinct names, including the company's garage. C is the number of broken cars. R is the number of roads in the city. Note that 0 < N < 100 , 0<=C < 1000 , and R < 10000 . The second line is made of C + 1 words, the first being the location of the company's garage, and the rest being the locations of the broken cars. A location is a word made of 10 letters or less. Letter case is significant. After the second line, there will be exactly R lines, each describing a road. A road is described using one of these three formats:


A -v -> B
A <-v - B
A <-v -> B


A and B are names of two different locations, while v is a positive integer (not exceeding 1000) denoting the length of the road. The first format specifies a one-way street from location A to B , the second specifies a one-way street from B to A , while the last specifies a two-way street between them. A , ``the arrow", and B are separated by one or more spaces. The end of the test cases is specified with a line having three zeros (for N , C , and R .)

The test case in the example below is the same as the one in the figure. 

 

Output
For each test case, print the total distance traveled using the following format:


k . V


Where k is test case number (starting at 1,) is a space, and V is the result.
 

Sample Input
4 2 5 NewTroy Midvale Metrodale NewTroy <-20-> Midvale Midvale --50-> Bakerline NewTroy <-5-- Bakerline Metrodale <-30-> NewTroy Metrodale --5-> Bakerline 0 0 0
 

Sample Output
1. 80

4个城市 2辆破车 5条路

收破车的公司在NewTroy 两辆破车分别在Midvale Metrodale

接下来为5条路 有单向也有双向

求回收所有破车的最小来回代价


思路:
用Floyd,注意输入处理,将字符串映射为数字


代码:

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstdlib>
#include<ctype.h>    //tower()
#include<set>  
#include<map>  
#include<iomanip>// cout<<setprecision(1)<<fixed<<a;
#include<vector>   
#include<cmath>	
#include<algorithm>
#include<bitset>
#include<limits.h>
#include<stack>
#include<queue>
using namespace std;
const int maxn=10000010;
const int inf=0x3f3f3f3f;

int n,c,m,a[105][105];
char save[1005][11];
map<string,int> mat;

void Floyd(){
    int i,j,k;
    for(i = 1;i<=n;i++)
        for(j = 1;j<=n;j++)
            for(k = 1;k<=n;k++)
                if(a[j][i]+a[i][k]<a[j][k])
                    a[j][k] = a[j][i]+a[i][k];
}

int main(){//124MS	1680K
    int val,cnt,sum,cas = 1;
    char s1[11],s2[11],s3[11];
    char from,to;
    while(scanf("%d%d%d",&n,&c,&m)==3&&(n+c+m)){
        sum = 0;
        mat.clear();
        memset(a,inf,sizeof(a));
        for(int i = 0; i<=c; i++) scanf("%s",save[i]);
        cnt = 1;
        for(int i = 0; i<m; i++){
            scanf("%s %c-%d-%c %s",s1,&from,&val,&to,s3);
            if(!mat[s1]) mat[s1] = cnt++;
            if(!mat[s3]) mat[s3] = cnt++;
            int x = mat[s1],y = mat[s3];
            if(from == '<' && val<a[y][x]) a[y][x] = val;//输入可能有重边 
            if(to == '>' && val<a[x][y]) a[x][y] = val;
        }
        Floyd();
        for(int i = 1; i<=c; i++) sum+=a[mat[save[0]]][mat[save[i]]]+a[mat[save[i]]][mat[save[0]]];
        printf("%d. %d\n",cas++,sum);
    }
    return 0;
}



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