Position of the K-th set bit in a number
Given two numbers N and K. The task is to find the index of the K-th set bit in the number from the right.
Note: Indexing in the binary representation starts from 0 from the right. For example in the binary number “000011”, the first set bit is at index 0 from right, and the second set bit is at index 1 from the right.
Examples:
Input: N = 15, K = 3 Output: 2 15 is "1111", hence the third bit is at index 2 from right. Input: N = 19, K = 2 Output: 1 19 is "10011", hence the second set bit is at inex 1 from right.
Approach: Initialize a counter 0, and increase it if the last bit is set in the number. For accessing the next bit, right shift the number by 1. When the counter’s value is equal to K, then we return the index of the number which was being incremented on every right shift.
Below is the implementation of the above approach:
C++
// C++ program to implement // the above approach #include <bits/stdc++.h> using namespace std; // Function that returns the Kth set bit int FindIndexKthBit(int n, int k) { int cnt = 0; int ind = 0; // Traverse in the binary while (n) { // Check if the last // bit is set or not if (n & 1) cnt++; // Check if count is equal to k // then return the index if (cnt == k) return ind; // Increase the index // as we move right ind++; // Right shift the number by 1 n = n >> 1; } return -1; } // Driver Code int main() { int n = 15, k = 3; int ans = FindIndexKthBit(n, k); if (ans != -1) cout << ans; else cout << "No k-th set bit"; return 0; } |
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Java
// Java program to implement // the above approach import java.util.*; class GFG { // Function that returns the Kth set bit static int FindIndexKthBit(int n, int k) { int cnt = 0; int ind = 0; // Traverse in the binary while (n > 0) { // Check if the last // bit is set or not if ((n & 1 ) != 0) cnt++; // Check if count is equal to k // then return the index if (cnt == k) return ind; // Increase the index // as we move right ind++; // Right shift the number by 1 n = n >> 1; } return -1; } // Driver Code public static void main(String args[]) { int n = 15, k = 3; int ans = FindIndexKthBit(n, k); if (ans != -1) System.out.println(ans); else System.out.println("No k-th set bit"); } } // This code is contributed by // Surendra_Gangwar |
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Python3
# Python3 implementation of the approach # Function that returns the Kth set bit def FindIndexKthBit(n, k): cnt, ind = 0, 0 # Traverse in the binary while n > 0: # Check if the last # bit is set or not if n & 1: cnt += 1 # Check if count is equal to k # then return the index if cnt == k: return ind # Increase the index # as we move right ind += 1 # Right shift the number by 1 n = n >> 1 return -1 # Driver Code if __name__ == "__main__": n, k = 15, 3 ans = FindIndexKthBit(n, k) if ans != -1: print(ans) else: print("No k-th set bit") # This code is contributed by # Rituraj Jain |
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C#
// C# program to implement // the above approach using System; class GFG { // Function that returns the Kth set bit static int FindIndexKthBit(int n, int k) { int cnt = 0; int ind = 0; // Traverse in the binary while (n > 0) { // Check if the last // bit is set or not if ((n & 1 ) != 0) cnt++; // Check if count is equal to k // then return the index if (cnt == k) return ind; // Increase the index // as we move right ind++; // Right shift the number by 1 n = n >> 1; } return -1; } // Driver Code public static void Main() { int n = 15, k = 3; int ans = FindIndexKthBit(n, k); if (ans != -1) Console.WriteLine(ans); else Console.WriteLine("No k-th set bit"); } } // This code is contributed by // Code_Mech. |
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PHP
<?php // PHP program to implement // the above approach // Function that returns the Kth set bit function FindIndexKthBit($n, $k) { $cnt = 0; $ind = 0; // Traverse in the binary while ($n) { // Check if the last // bit is set or not if ($n & 1) $cnt++; // Check if count is equal to k // then return the index if ($cnt == $k) return $ind; // Increase the index // as we move right $ind++; // Right shift the number by 1 $n = $n >> 1; } return -1; } // Driver Code $n = 15; $k = 3; $ans = FindIndexKthBit($n, $k); if ($ans != -1) echo $ans; else echo "No k-th set bit"; // This code is contributed by Ryuga ?> |
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Output:
2
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