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use strict;
use warnings;
...
        }
    }
}

$ perl N_among_M.pl
1 2 3
...
2 3 5
2 4 5
3 4 5

$ perl N_among_M.pl
1 2 3 4
...
6 7 9 10
6 8 9 10
7 8 9 10

$ time perl N_among_M.pl
167960
...
user    0m0.499s
sys     0m0.015s