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

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

## Recommended: Please solve it on “__PRACTICE__ ” first, before moving on to the solution.

__PRACTICE__## C#

`// C# program to count all distinct binary` `// strings without two consecutive 1's` `using` `System;` ` ` `class` `Subset_sum {` ` ` `static` `int` `countStrings(` `int` `n)` ` ` `{` ` ` `int` `[] a = ` `new` `int` `[n];` ` ` `int` `[] b = ` `new` `int` `[n];` ` ` `a[0] = b[0] = 1;` ` ` `for` `(` `int` `i = 1; i < n; i++) {` ` ` `a[i] = a[i - 1] + b[i - 1];` ` ` `b[i] = a[i - 1];` ` ` `}` ` ` `return` `a[n - 1] + b[n - 1];` ` ` `}` ` ` ` ` `// Driver Code` ` ` `public` `static` `void` `Main()` ` ` `{` ` ` `Console.Write(countStrings(3));` ` ` `}` `}` ` ` `// This code is contributed by nitin mittal` |

**Output:**

5

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