Bit manipulation is a powerful technique in programming, especially when dealing with binary data. In C++, the bitset class provides a convenient way to handle a fixed-size sequence of bits. If you have a bitset and you need to find the first occurrence of a specific bit pattern, there are several approaches you can take. In this blog post, we will discuss a simple and efficient method to accomplish this task.

The Problem

Let’s say you have a bitset object named bits and you want to find the index of the first occurrence of a specific bit pattern represented by another bitset object named pattern. You want to find the leftmost occurrence of the pattern within bits.

The Solution

To solve this problem, we can iterate over the bits of the bitset bits and use a sliding window approach to check for a match with the pattern. Here’s an example implementation in C++:

#include <bitset>

int findFirstOccurrence(const std::bitset<N>& bits, const std::bitset<N>& pattern) {
    for (int i = 0; i <= bits.size() - pattern.size(); i++) {
        if ((bits >> i) == pattern) {
            return i;
        }
    }
    return -1; // Return -1 if pattern is not found
}

In the code above, we define a function findFirstOccurrence that takes two bitset objects bits and pattern, both of size N. We iterate over the bits of bits starting from index 0 until bits.size() - pattern.size() and for each position, we shift bits to the right by i bits and check if it matches with pattern. If we find a match, we return the index i. If no match is found, we return -1.

Example Usage

#include <iostream>

int main() {
    std::bitset<8> bits("10110010");
    std::bitset<3> pattern("101");

    int index = findFirstOccurrence(bits, pattern);

    if (index != -1) {
        std::cout << "Pattern found at index " << index << std::endl;
    } else {
        std::cout << "Pattern not found" << std::endl;
    }

    return 0;
}

In this example, we define bits as a bitset object representing the binary string “10110010” and pattern as a bitset object representing the binary string “101”. We pass these objects to the findFirstOccurrence function and store the returned index in the index variable. Finally, we print the result based on whether the index is -1 or not.

Conclusion

In this blog post, we have discussed a simple and efficient method to find the first occurrence of a specific bit pattern within a bitset in C++. By using a sliding window approach and bit shifting, we can efficiently search for the desired pattern. This technique can be useful when working with binary data and performing bit-level operations.

#programming #C++