POJ1125 Stockbroker Grapevine 【Floyd】

Stockbroker Grapevine

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

题意：以输入数据为例，有n个人，对于每i个人给定一行数据：k,v,dis,v,dis...表示第i个人能跟k个人联络，然后给出这k个人的编号和与其联系的时间dis，求选定一个人作为消息源将消息进行扩散，直到所有人都收到消息，输出选定的人的编号以及消息传递的最短时间。

题解：用Floyd求出任意两点间的距离，然后遍历每个人能联系到的人的最长距离，如果没有一个人能联系所有人，那么输出disjoint。

#include <stdio.h>
#include <string.h>
#include <algorithm>

#define maxn 102
#define inf 0x3f3f3f3f

int map[maxn][maxn];

void getMap(int n) {
    int i, j, k, u, v, dis;
    memset(map, 0x3f, sizeof(map));
    for(u = 1; u <= n; ++u) {
        map[u][u] = 0;
        scanf("%d", &k);
        while(k--) {
            scanf("%d%d", &v, &dis);
            map[u][v] = dis;
        }
    }
}

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

void solve(int n) {
    Floyd(n);
    int i, ans_val = inf, ans_pos = 0, *p;
    for(i = 1; i <= n; ++i) {
        p = std::max_element(map[i] + 1, map[i] + n + 1);
        if(*p != inf && *p < ans_val) {
            ans_val = *p; ans_pos = i;
        }
    }
    if(!ans_pos) printf("disjoint\n");
    else printf("%d %d\n", ans_pos, ans_val);
}

int main() {
    // freopen("stdin.txt", "r", stdin);
    int n;
    while(scanf("%d", &n), n) {
        getMap(n);
        solve(n);
    }
    return 0;
}