[floyd]POJ 1603 Risk

传送门：Risk

Description

Risk is a board game in which several opposing players attempt to conquer the world. The gameboard consists of a world map broken up into hypothetical countries. During a player's turn, armies stationed in one country are only allowed to attack only countries with which they share a common border. Upon conquest of that country, the armies may move into the newly conquered country. 

During the course of play, a player often engages in a sequence of conquests with the goal of transferring a large mass of armies from some starting country to a destination country. Typically, one chooses the intervening countries so as to minimize the total number of countries that need to be conquered. Given a description of the gameboard with 20 countries each with between 1 and 19 connections to other countries, your task is to write a function that takes a starting country and a destination country and computes the minimum number of countries that must be conquered to reach the destination. You do not need to output the sequence of countries, just the number of countries to be conquered including the destination. For example, if starting and destination countries are neighbors, then your program should return one. 

The following connection diagram illustrates the first sample input. 

Input

Output

Sample Input

1 3
2 3 4
3 4 5 6
1 6
1 7
2 12 13
1 8
2 9 10
1 11
1 11
2 12 17
1 14
2 14 15
2 15 16
1 16
1 19
2 18 19
1 20
1 20
5
1 20
2 9
19 5
18 19
16 20

Sample Output

Test Set #1
1 to 20: 7
2 to 9: 5
19 to 5: 6
18 to 19: 2
16 to 20: 2

Source

解题报告:

此题可用floyd做，代码如下：

#include<iostream>
#include<cstdio>
#define INF 1000
using namespace std;
int weight[30][30];
int n;
void floyd(){
    for(int t=1;t<=20;t++)
        for(int i=1;i<=20;i++)
            for(int j=1;j<=20;j++)
                weight[i][j]=min(weight[i][j],weight[i][t]+weight[t][j]);
}
int main(){
    int k=0;
    while(scanf("%d",&n)==1){
        for(int i=0;i<30;i++){
            for(int j=0;j<30;j++)
                weight[i][j]=INF;
            weight[i][i]=0;
        }
        int v;
        for(int i=0;i<n;i++){
            scanf("%d",&v);
            weight[1][v]=weight[v][1]=1;
        }
        for(int i=2;i<20;i++){
            scanf("%d",&n);
            for(int j=0;j<n;j++){
                scanf("%d",&v);
                weight[i][v]=weight[v][i]=1;
            }
        }
        floyd();
        scanf("%d",&v);
        int x,y;
        printf("Test Set #%dn",++k);
        for(int i=0;i<v;i++){
            scanf("%d%d",&x,&y);
            printf("%d to %d: %dn",x,y,weight[x][y]);
        }
        printf("n");
    }
    return 0;
}

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