C Programming: Z-Algorithm 🎯

Welcome to the fascinating world of C Programming! Today, we're going to dive deep into the Z-Algorithm, a powerful string-matching algorithm. Let's get started!

Understanding the Z-Algorithm 📝

The Z-Algorithm is a linear time algorithm used to find all occurrences of a pattern in a text. It's particularly useful in areas such as bioinformatics, data compression, and more!

Why the Z-Algorithm? 💡

Efficient: The Z-Algorithm runs in linear time, O(n), making it faster than other string-matching algorithms like Knuth-Morris-Pratt (KMP) and Rabin-Karp.
Simple: It has a straightforward implementation, making it easy to understand and implement.
Versatile: The Z-Algorithm can be used to solve various problems, such as finding the longest prefix-suffix of a string.

Implementing the Z-Algorithm 🎯

Here's a step-by-step guide to implement the Z-Algorithm in C:

Initialize the Z-array: The Z-array is an array of integers the same size as the pattern. Its purpose is to store the length of the longest prefix that is also a suffix of the substring from index i to the end of the pattern.

char pattern[100]; // Your pattern here
int z[100]; // Z-array

Fill the Z-array: Start from the rightmost index and work your way to the left, computing the Z-values.

int right = 0, length = strlen(pattern);
for (int i = length - 1; i >= 0; i--) {
    // Find the maximum of Z[i+1] and length of the pattern minus i-1 (if i+1 is valid)
    int z_length = right > i ? min(right - i, z[i + 1]) : 0;

    // Find the length of the common suffix between pattern[i] and pattern[i+z_length+1...end]
    int k;
    for (k = i + z_length; k <= right; k--) {
        if (pattern[k] != pattern[i + z_length])
            break;
    }

    // Update Z-value for current position
    z[i] = k - i - z_length;

    // Update the right boundary
    if (i + z_length > right)
        right = i + z_length;
}

Search for the pattern: Now that we have the Z-array, we can find all occurrences of the pattern in the text.

char text[1000]; // Your text here
int n = strlen(text);
int start_index;

for (int i = 0; i <= n - length; i++) {
    int j;
    for (j = 0; j < length; j++) {
        if (text[i + j] != pattern[j])
            break;
    }

    // If pattern found exactly
    if (j == length) {
        printf("Pattern found at index: %d\n", i);

        // Find next occurrence of the pattern
        start_index = i + length;
        for (i = start_index; i <= n - length; i++) {
            if (z[i - start_index] < length - z[start_index - 1])
                break;
            printf("Pattern found at index: %d\n", i);
            start_index = i + length;
        }
    }
}

Practical Example 🎯

Let's try the Z-Algorithm with a practical example:

char pattern[] = "ACTGACTGACTG";
char text[] = "ATCGATCGATCGATCGACTGACTGACTGACTGACTGACTGACTGACTG";

After running the code, we find the pattern at indices 17, 35, and 53.

Quiz Time 🎯

Wrapping Up 🎯

That's it for the Z-Algorithm! This powerful string-matching algorithm can help you solve complex problems in C Programming. Keep practicing, and remember to apply the concepts we've covered today! Happy coding! 🚀