 Open in App
Not now

# Python Program to Count number of binary strings without consecutive 1’s

• Last Updated : 16 Jun, 2022

Given a positive integer N, count all possible distinct binary strings of length N such that there are no consecutive 1’s.

Examples:

```Input:  N = 2
Output: 3
// The 3 strings are 00, 01, 10

Input: N = 3
Output: 5
// The 5 strings are 000, 001, 010, 100, 101```

## Python3

 `# Python program to count``# all distinct binary strings``# without two consecutive 1's` `def` `countStrings(n):` `    ``a ``=``[``0` `for` `i ``in` `range``(n)]``    ``b ``=``[``0` `for` `i ``in` `range``(n)]``    ``a[``0``] ``=` `b[``0``] ``=` `1``    ``for` `i ``in` `range``(``1``, n):``        ``a[i] ``=` `a[i``-``1``] ``+` `b[i``-``1``]``        ``b[i] ``=` `a[i``-``1``]``    ` `    ``return` `a[n``-``1``] ``+` `b[n``-``1``]` `# Driver program to test``# above functions` `print``(countStrings(``3``))` `# This code is contributed``# by Anant Agarwal.`

Output:

```5
```

Time Complexity: O(n)
Auxiliary Space: O(n)

Please refer complete article on Count number of binary strings without consecutive 1’s for more details!

My Personal Notes arrow_drop_up