Calculate the Levenshtein edit distance in C

This is an example C program demonstrating the calculation of the Levenshtein edit distance. This example uses the naive dynamic programming algorithm.

#include <string.h>
#include <stdio.h>

static int distance (const char * word1,
                     int len1,
                     const char * word2,
                     int len2)
{
    int matrix[len1 + 1][len2 + 1];
    int i;
    for (i = 0; i <= len1; i++) {
        matrix[i][0] = i;
    }
    for (i = 0; i <= len2; i++) {
        matrix[0][i] = i;
    }
    for (i = 1; i <= len1; i++) {
        int j;
        char c1;

        c1 = word1[i-1];
        for (j = 1; j <= len2; j++) {
            char c2;

            c2 = word2[j-1];
            if (c1 == c2) {
                matrix[i][j] = matrix[i-1][j-1];
            }
            else {
                int delete;
                int insert;
                int substitute;
                int minimum;

                delete = matrix[i-1][j] + 1;
                insert = matrix[i][j-1] + 1;
                substitute = matrix[i-1][j-1] + 1;
                minimum = delete;
                if (insert < minimum) {
                    minimum = insert;
                }
                if (substitute < minimum) {
                    minimum = substitute;
                }
                matrix[i][j] = minimum;
            }
        }
    }
    return matrix[len1][len2];
}

int main ()
{
    const char * word1;
    const char * word2;
    int len1;
    int len2;
    int d;

    word1 = "pieces";
    word2 = "paces";
    len1 = strlen (word1);
    len2 = strlen (word2);
    d = distance (word1, len1, word2, len2);
    printf ("The edit distance between %s and %s is %d.\n",
            word1, word2, d);
    return 0;
}

Download it here.

The output of the example looks like this:

The edit distance between pieces and paces is 2.


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