1034. Head of a Gang (30)

One way that the police finds the head of a gang is to check people's phone calls. If there is a phone call between A and B, we say that A and B is related. The weight of a relation is defined to be the total time length of all the phone calls made between the two persons. A "Gang" is a cluster of more than 2 persons who are related to each other with total relation weight being greater than a given threthold K. In each gang, the one with maximum total weight is the head. Now given a list of phone calls, you are supposed to find the gangs and the heads.

Input Specification:

Each input file contains one test case. For each case, the first line contains two positive numbers N and K (both less than or equal to 1000), the number of phone calls and the weight threthold, respectively. Then N lines follow, each in the following format:

Name1 Name2 Time

where Name1 and Name2 are the names of people at the two ends of the call, and Time is the length of the call. A name is a string of three capital letters chosen from A-Z. A time length is a positive integer which is no more than 1000 minutes.

Output Specification:

For each test case, first print in a line the total number of gangs. Then for each gang, print in a line the name of the head and the total number of the members. It is guaranteed that the head is unique for each gang. The output must be sorted according to the alphabetical order of the names of the heads.

Sample Input 1:

8 59
AAA BBB 10
BBB AAA 20
AAA CCC 40
DDD EEE 5
EEE DDD 70
FFF GGG 30
GGG HHH 20
HHH FFF 10

Sample Output 1:

2
AAA 3
GGG 3

Sample Input 2:

8 70
AAA BBB 10
BBB AAA 20
AAA CCC 40
DDD EEE 5
EEE DDD 70
FFF GGG 30
GGG HHH 20
HHH FFF 10

Sample Output 2:

0

http://pat.zju.edu.cn/contests/pat-a-practise/1034

题意

『gang』翻译过来是『一伙人』。gang 的定义是一群人，至少有 3 个人，这群人中每个人之间都通过通话相连，且整个群体的通话时长超过一个阈值。整个 gang 的团体中，拥有的电话时长最长的人就是头目了。

题目给定了 gang 的阈值 K，以及 N 个通话记录，每条记录包括主叫人、被叫人以及通话时间。要求计算出有几个 gang，并按照 gang 的头目的字母顺序排序输出头目和其中成员数量。

分析

本题使用 dfs 求解比较方便。dfs 能简单的实现状态值的记录，比如当前的 gang 的成员数量和权重，如果使用并查集，则相对复杂。

需要注意的坑点：如果建立邻接表时，每个通话记录都在两人头上计算了时间积累的，那么在判定 gang 的权重值是否低于阈值的时候，需要对阈值乘以 2。