Levenshtein distance matrix construction

levenshtein_tab.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define MIN3(a, b, c) ((a) < (b) ? ((a) < (c) ? (a) : (c)) : ((b) < (c) ? (b) : (c)))

int* min_edit_distance_tab(char *source, char *target, int ins_cost, int del_cost, int rep_cost)
{
    /*
    Input: 
        source: a string corresponding to the string you are starting with
        target: a string corresponding to the string you want to end with
        ins_cost: an integer setting the insert cost
        del_cost: an integer setting the delete cost
        rep_cost: an integer setting the replace cost
    Output:
        D: a matrix of len(source)+1 by len(target)+1 containing minimum edit distances
    */

    // use deletion and insert cost as  1
    int nb_row = strlen(source)+1;
    int nb_col = strlen(target)+1;
    int row, col;
    int r_cost;
    int replace, delete, insert;
    // distance matrix
    int D[nb_row * nb_col];
        
    // initialize cost matrix    
    D[0] = 0;
    
    for (row=1; row<nb_row; row++)
        D[row*nb_col] = D[(row-1)*nb_col] + del_cost;

    for (col=1; col<nb_col; col++)
        D[col] = D[col-1] + ins_cost;

    for (row=1; row<nb_row; row++)
        for (col=1; col<nb_col; col++)
        {
            // Intialize r_cost to the 'replace' cost that is passed into this function
            r_cost = rep_cost;

            // Check to see if source character at the previous row
            // matches the target character at the previous column, 
            if(source[row-1] == target[col-1])
            {
                // Update the replacement cost to 0 if source and target are the same
                r_cost = 0;
            }

            // Update the cost at row, col based on previous entries in the cost matrix
            // Refer to the equation calculate for D[i,j] (the minimum of three calculated costs)
            replace = D[(row-1)*nb_col + col-1] + r_cost;
            delete = D[(row-1)*nb_col + col] + del_cost;
            insert = D[row*nb_col + col-1] + ins_cost;
            D[row*nb_col + col] = MIN3(replace, delete, insert);              
        }
    return D;
}