# Python Program for Number of stopping station problem

• Difficulty Level : Medium
• Last Updated : 03 Dec, 2018

There are 12 intermediate stations between two places A and B. Find the number of ways in which a train can be made to stop at 4 of these intermediate stations so that no two stopping stations are consecutive?

Examples –

```Input  : n = 12, s = 4
Output : 126

Input  : n = 16, s = 5
Output : 792
```

 `# Python code to calculate number``# of ways of selecting \'p\' non ``# consecutive stations out of ``# \'n\' stations`` ` `def` `stopping_station( p, n):``    ``num ``=` `1``    ``dem ``=` `1``    ``s ``=` `p`` ` `    ``# selecting \'s\' positions``    ``# out of \'n-s+1\'``    ``while` `p !``=` `1``:``        ``dem ``*``=` `p``        ``p``-``=``1``     ` `    ``t ``=` `n ``-` `s ``+` `1``    ``while` `t !``=` `(n``-``2` `*` `s ``+` `1``):``        ``num ``*``=` `t``        ``t``-``=``1``    ``if` `(n ``-` `s ``+` `1``) >``=` `s:``        ``return` `int``(num``/``dem)``    ``else``:``        ``# if conditions does not``        ``# satisfy of combinatorics``        ``return` `-``1`` ` `# driver code ``num ``=` `stopping_station(``4``, ``12``)``if` `num !``=` `-``1``:``    ``print``(num)``else``:``    ``print``(``"Not Possible"``)`` ` `# This code is contributed by "Abhishek Sharma 44"`

Output :

```126
```

Please refer complete article on Number of stopping station problem for more details!

My Personal Notes arrow_drop_up