# 1 to n bit numbers with no consecutive 1s in binary representation

Given a number n, our task is to find all 1 to n bit numbers with no consecutive 1s in their binary representation.**Examples:**

Input:N = 4Output:1 2 4 5 8 9 10 These are numbers with 1 to 4 bits and no consecutive ones in binary representation.Input:n = 3Output:1 2 4 5

**Approach:**

- There will be 2
^{n}numbers with number of bits from 1 to n. - Iterate through all 2
^{n}numbers. For every number check if it contains consecutive set bits or not. To check, we do bitwise and of current number i and left-shifted i. If the bitwise and contains a non-zero bit (or its value is non-zero), then the given number contains consecutive set bits.

Below is the implementation of the above approach:

## C++

`// Print all numbers upto n bits` `// with no consecutive set bits.` `#include<iostream>` `using` `namespace` `std;` `void` `printNonConsecutive(` `int` `n)` `{` ` ` `// Let us first compute` ` ` `// 2 raised to power n.` ` ` `int` `p = (1 << n);` ` ` `// loop 1 to n to check` ` ` `// all the numbers` ` ` `for` `(` `int` `i = 1; i < p; i++)` ` ` `// A number i doesn't contain` ` ` `// consecutive set bits if` ` ` `// bitwise and of i and left` ` ` `// shifted i do't contain a` ` ` `// commons set bit.` ` ` `if` `((i & (i << 1)) == 0)` ` ` `cout << i << ` `" "` `;` `}` `// Driver code` `int` `main()` `{` ` ` `int` `n = 3;` ` ` `printNonConsecutive(n);` ` ` `return` `0;` `}` |

## Java

`// Java Code to Print all numbers upto` `// n bits with no consecutive set bits.` `import` `java.util.*;` `class` `GFG` `{` ` ` `static` `void` `printNonConsecutive(` `int` `n)` ` ` `{` ` ` `// Let us first compute` ` ` `// 2 raised to power n.` ` ` `int` `p = (` `1` `<< n);` ` ` `// loop 1 to n to check` ` ` `// all the numbers` ` ` `for` `(` `int` `i = ` `1` `; i < p; i++)` ` ` `// A number i doesn't contain` ` ` `// consecutive set bits if` ` ` `// bitwise and of i and left` ` ` `// shifted i do't contain a` ` ` `// commons set bit.` ` ` `if` `((i & (i << ` `1` `)) == ` `0` `)` ` ` `System.out.print(i + ` `" "` `);` ` ` ` ` `}` `// Driver code` `public` `static` `void` `main(String[] args)` ` ` `{` ` ` `int` `n = ` `3` `;` ` ` `printNonConsecutive(n);` ` ` `}` `}` `// This code is contributed by Mr. Somesh Awasthi` |

## Python3

`# Python3 program to print all numbers upto` `# n bits with no consecutive set bits.` `def` `printNonConsecutive(n):` ` ` `# Let us first compute ` ` ` `# 2 raised to power n.` ` ` `p ` `=` `(` `1` `<< n)` ` ` `# loop 1 to n to check` ` ` `# all the numbers` ` ` `for` `i ` `in` `range` `(` `1` `, p):` ` ` `# A number i doesn't contain` ` ` `# consecutive set bits if` ` ` `# bitwise and of i and left` ` ` `# shifted i do't contain a` ` ` `# common set bit.` ` ` `if` `((i & (i << ` `1` `)) ` `=` `=` `0` `):` ` ` `print` `(i, end ` `=` `" "` `)` `# Driver code` `n ` `=` `3` `printNonConsecutive(n)` `# This code is contributed by Anant Agarwal.` |

## C#

`// C# Code to Print all numbers upto` `// n bits with no consecutive set bits.` `using` `System;` `class` `GFG` `{` ` ` `static` `void` `printNonConsecutive(` `int` `n)` ` ` `{` ` ` `// Let us first compute` ` ` `// 2 raised to power n.` ` ` `int` `p = (1 << n);` ` ` `// loop 1 to n to check` ` ` `// all the numbers` ` ` `for` `(` `int` `i = 1; i < p; i++)` ` ` `// A number i doesn't contain` ` ` `// consecutive set bits if` ` ` `// bitwise and of i and left` ` ` `// shifted i do't contain a` ` ` `// commons set bit.` ` ` `if` `((i & (i << 1)) == 0)` ` ` `Console.Write(i + ` `" "` `);` ` ` ` ` `}` `// Driver code` `public` `static` `void` `Main()` ` ` `{` ` ` `int` `n = 3;` ` ` `printNonConsecutive(n);` ` ` `}` `}` `// This code is contributed by nitin mittal.` |

## PHP

`<?php` `// Print all numbers upto n bits` `// with no consecutive set bits.` `function` `printNonConsecutive(` `$n` `)` `{` ` ` ` ` `// Let us first compute` ` ` `// 2 raised to power n.` ` ` `$p` `= (1 << ` `$n` `);` ` ` `// loop 1 to n to check` ` ` `// all the numbers` ` ` `for` `(` `$i` `= 1; ` `$i` `< ` `$p` `; ` `$i` `++)` ` ` `// A number i doesn't contain` ` ` `// consecutive set bits if` ` ` `// bitwise and of i and left` ` ` `// shifted i do't contain a` ` ` `// commons set bit.` ` ` `if` `((` `$i` `& (` `$i` `<< 1)) == 0)` ` ` `echo` `$i` `. ` `" "` `;` `}` ` ` `// Driver code` ` ` `$n` `= 3;` ` ` `printNonConsecutive(` `$n` `); ` ` ` `// This code is contributed by Sam007` `?>` |

## Javascript

`<script>` `// Javascript Code to Print all numbers upto` `// n bits with no consecutive set bits.` `function` `printNonConsecutive(n)` ` ` `{` ` ` `// Let us first compute` ` ` `// 2 raised to power n.` ` ` `let p = (1 << n);` ` ` `// loop 1 to n to check` ` ` `// all the numbers` ` ` `for` `(let i = 1; i < p; i++)` ` ` `// A number i doesn't contain` ` ` `// consecutive set bits if` ` ` `// bitwise and of i and left` ` ` `// shifted i do't contain a` ` ` `// commons set bit.` ` ` `if` `((i & (i << 1)) == 0)` ` ` `document.write(i + ` `" "` `);` ` ` ` ` `}` `// driver program` ` ` `let n = 3;` ` ` `printNonConsecutive(n);` ` ` `</script>` |

**Output**

1 2 4 5

**Time Complexity: **O(2^{N})**Auxiliary Space: **O(1)

This article is contributed by **Devanshu Agarwal**. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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