POJ 1125 Stockbroker Grapevine

Stockbroker Grapevine

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 33259		Accepted: 18323

Description

Stockbrokers are known to overreact to rumours. You have been contracted to develop a method of spreading disinformation amongst the stockbrokers to give your employer the tactical edge in the stock market. For maximum effect, you have to spread the rumours in the fastest possible way.

Unfortunately for you, stockbrokers only trust information coming from their "Trusted sources" This means you have to take into account the structure of their contacts when starting a rumour. It takes a certain amount of time for a specific stockbroker to pass the rumour on to each of his colleagues. Your task will be to write a program that tells you which stockbroker to choose as your starting point for the rumour, as well as the time it will take for the rumour to spread throughout the stockbroker community. This duration is measured as the time needed for the last person to receive the information.

Input

Your program will input data for different sets of stockbrokers. Each set starts with a line with the number of stockbrokers. Following this is a line for each stockbroker which contains the number of people who they have contact with, who these people are, and the time taken for them to pass the message to each person. The format of each stockbroker line is as follows: The line starts with the number of contacts (n), followed by n pairs of integers, one pair for each contact. Each pair lists first a number referring to the contact (e.g. a '1' means person number one in the set), followed by the time in minutes taken to pass a message to that person. There are no special punctuation symbols or spacing rules.

Each person is numbered 1 through to the number of stockbrokers. The time taken to pass the message on will be between 1 and 10 minutes (inclusive), and the number of contacts will range between 0 and one less than the number of stockbrokers. The number of stockbrokers will range from 1 to 100. The input is terminated by a set of stockbrokers containing 0 (zero) people.

Output

For each set of data, your program must output a single line containing the person who results in the fastest message transmission, and how long before the last person will receive any given message after you give it to this person, measured in integer minutes.
It is possible that your program will receive a network of connections that excludes some persons, i.e. some people may be unreachable. If your program detects such a broken network, simply output the message "disjoint". Note that the time taken to pass the message from person A to person B is not necessarily the same as the time taken to pass it from B to A, if such transmission is possible at all.

Sample Input

3
2 2 4 3 5
2 1 2 3 6
2 1 2 2 2
5
3 4 4 2 8 5 3
1 5 8
4 1 6 4 10 2 7 5 2
0
2 2 5 1 5
0

Sample Output

3 2
3 10

Source

Southern African 2001

 

 

 

解析：题目要求从某一结点开始，能让消耗的总时间最短。实际上这是一个在有向图中求最短路径问题，先求出每个人向其他人发消息所用的最短时间（当然不是每个人都能向所有人发消息的），然后在所有能向每个人发消息的人中比较他们所用的最大时间，找出所用最大时间最小的那一个即为所求。用Floyd算法即可。

 

 

 

#include <cstdio>

const int INF = 0x3f3f3f3f;
int n;
int e[105][105];

void floyd()
{
    for(int i = 1; i <= n; ++i){
        for(int j = 1; j <= n; ++j){
            if(i == j)
                e[i][j] = 0;
            else
                e[i][j] = INF;
        }
    }
    for(int i = 1; i <= n; ++i){
        int num, j, val;
        scanf("%d", &num);
        while(num--){
            scanf("%d%d", &j, &val);
            e[i][j] = val;
        }
    }
    for(int k = 1; k <= n; ++k){
        for(int i = 1; i <= n; ++i){
            for(int j = 1; j <= n; ++j)
                if(e[i][k]+e[k][j]<e[i][j])
                    e[i][j] = e[i][k]+e[k][j];
        }
    }
}

int main()
{
    while(scanf("%d", &n), n){
        floyd();
        int person = 0;
        int time = INF;
        for(int i = 1; i <= n; ++i){
            int tmp = 0;
            for(int j = 1; j <= n; ++j){
                if(e[i][j]>tmp)
                    tmp = e[i][j];
            }
            if(tmp<time){
                time = tmp;
                person = i;
            }
        }
        if(person != 0)
            printf("%d %d
", person, time);
        else
            printf("disjoint
");
    }
    return 0;
}