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Problems

Median Tree

Median Tree

You are given a connected undirected graph which has even numbers of nodes. A connected graph is a graph in which all nodes are connected directly or indirectly by edges. Your task is to find a spanning tree whose median value of edges' costs is minimum. A spanning tree of a graph means that a tree which contains all nodes of the graph. \InputFile The input consists of multiple datasets. The format of each dataset is as follows. \textbf{n m} \textbf{s_1 t_1 c_1} \textbf{...} \textbf{s_m t_m c_m} The fi rst line contains an even number \textbf{n} (\textbf{2} ≤ \textbf{n} ≤ \textbf{1000}) and an integer \textbf{m} (\textbf{n-1} ≤ \textbf{m} ≤ \textbf{10000}). \textbf{n} is the nubmer of nodes and \textbf{m} is the number of edges in the graph. Then \textbf{m} lines follow, each of which contains \textbf{s_i} (\textbf{1} ≤ \textbf{s_i} ≤ \textbf{n}), \textbf{t_i} (\textbf{1} ≤ \textbf{s_i} ≤ \textbf{n}, \textbf{t_i} ≠ \textbf{s_i}) and \textbf{c_i} (\textbf{1} ≤ \textbf{c_i} ≤ \textbf{1000}). This means there is an edge between the nodes \textbf{s_i} and \textbf{t_i} and its cost is \textbf{c_i}. There is no more than one edge which connects \textbf{s_i} and \textbf{t_i}. The input terminates when \textbf{n = 0} and \textbf{m = 0}. Your program must not output anything for this case. \OutputFile Print the median value in a line for each dataset.
Time limit 1 second
Memory limit 256 MiB
Input example #1
2 1
1 2 5
4 6
1 2 1
1 3 2
1 4 3
2 3 4
2 4 5
3 4 6
8 17
1 4 767
3 1 609
8 3 426
6 5 972
8 1 607
6 4 51
5 1 683
3 6 451
3 4 630
8 7 912
3 7 43
4 7 421
3 5 582
8 4 538
5 7 832
1 6 345
8 2 608
0 0
Output example #1
5
2
421
Source JAG Practice Contest for ACM-ICPC Asia Regional 2012, AtCoder, 2012/11/04