Set the Left most unset bit

Given an integer, set the leftmost unset bit. Leftmost unset bit is the first unset bit after most significant set bit. If all bits (after most significant set bit) are set, then return the number.

Examples:

Input : 10
Output : 14
10 = 1 0 1 0    // 10 binary
14 = 1 1 1 0    // after set left most unset bit

Input : 15
Output : 15
15 = 1 1 1 1    // 15 binary
15 = 1 1 1 1    // because all bits are set

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:-
1. Return the number if all bits are set.
2. Traverse all the bit to get the last unset bit.
3. Take OR with the original number and the unset bit.

Below is the implementation of the approach.

C++

 // CPP program to set the leftmost unset bit #include using namespace std;    // set left most unset bit int setleftmostunsetbit(int n) {     // if number contain all     // 1 then return n     if ((n & (n + 1)) == 0)         return n;        // Find position of leftmost unset bit.     int pos = 0;     for (int temp=n, count=0; temp>0;                         temp>>=1, count++)            // if temp L.S.B is zero         // then unset bit pos is         // change         if ((temp & 1) == 0)              pos = count;           // return OR of number and     // unset bit pos     return (n | (1 << (pos))); }    // Driver Function int main() {     int n = 10;     cout << setleftmostunsetbit(n);     return 0; }

Java

 // Java program to set  // the leftmost unset bit import java.io.*;    class GFG  {     // set left most unset bit     static int setleftmostunsetbit(int n)     {         // if number contain all         // 1 then return n         if ((n & (n + 1)) == 0)             return n;                // Find position of leftmost unset bit.         int pos = 0;         for (int temp = n, count = 0; temp > 0;                            temp >>= 1, count++)                    // if temp L.S.B is zero             // then unset bit pos is             // change             if ((temp & 1) == 0)                  pos = count;                 // return OR of number and         // unset bit pos         return (n | (1 << (pos)));     }            // Driver Function     public static void main (String[] args)      {         int n = 10;         System.out.println(setleftmostunsetbit(n));     } }    // This code is contributed by Ansu Kumari

Python3

 # Python program to set the leftmost unset bit    # Set left most unset bit def setleftmostunsetbit(n):     # if number contain all     # 1 then return n     if not (n & (n + 1)):         return n        # Find position of leftmost unset bit     pos, temp, count = 0, n, 0            while temp:         # if temp L.S.B is zero         # then unset bit pos is         # change         if not (temp & 1):             pos = count                         count += 1; temp>>=1        # return OR of number and     # unset bit pos     return (n | (1 << (pos)))       # Driver Function n = 10 print(setleftmostunsetbit(n))    # This code is contributed by Ansu Kumari

C#

 // C# program to set  // the leftmost unset bit using System;    class GFG  {     // set left most unset bit     static int setleftmostunsetbit(int n)     {         // if number contain all         // 1 then return n         if ((n & (n + 1)) == 0)             return n;                // Find position of leftmost unset bit.         int pos = 0;         for (int temp = n, count = 0; temp > 0;                             temp >>= 1, count++)                    // if temp L.S.B is zero             // then unset bit pos is             // change             if ((temp & 1) == 0)                  pos = count;                 // return OR of number and         // unset bit pos         return (n | (1 << (pos)));     }            // Driver Function     public static void Main ()      {         int n = 10;         Console.WriteLine(setleftmostunsetbit(n));     } }    // This code is contributed by vt_m

PHP

 0;                      \$temp >>= 1, \$count++)            // if temp L.S.B is zero         // then unset bit pos is         // change         if ((\$temp & 1) == 0)              \$pos = \$count;         // return OR of number      // and unset bit pos     return (\$n | (1 << (\$pos))); }        // Driver code     \$n = 10;     echo setleftmostunsetbit(\$n);    //This code is contributed by mits  ?>

Output:

14

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