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C/C++ Program to Count number of binary strings without consecutive 1’s
  • Last Updated : 02 Jan, 2019

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.

C++




// C++ program to count all distinct binary strings
// without two consecutive 1's
#include <iostream>
using namespace std;
  
int countStrings(int n)
{
    int a[n], b[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 program to test above functions
int main()
{
    cout << countStrings(3) << endl;
    return 0;
}


Output:

5

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

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