Easy Knuth–Morris–Pratt (KMP) with C

main.c

//just new to C
//other example: http://code.activestate.com/recipes/577908-implementation-of-knuthmorrispratt-algorithm/
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <memory.h>

bool is_substring(const char *haystack, const char *needle) {
    int m=0, i=0;
    int hsize = strlen(haystack);
    int nsize = strlen(needle);

    //prefix table
    int *pt = malloc(sizeof(int) * nsize);

    for (i = 1; i < nsize; i++) {
        if (needle[i] == needle[m]) {
            m++;
        } else {
            m=0;
        }
        pt[i]=m;
    }

    //find match
    m=0;
    i=0;
    while(m + i < hsize) {
        if (haystack[m + i] == needle[i]) {
            if (i+1 == nsize) {
                free(pt);
                return true;
            } else {
                i++;
            }
        } else {
            if (pt[i-1] != 0) {
                m = m + i - pt[i-1];
                i = pt[i-1];
            } else {
                m += i + 1;
                i = 0;
            }
        }

    }

    free(pt);
    return false;
}

int main() {
    printf("Hello, World!\n");
    char target[] = "ABC ABCDAB ABCDABCDABDE";
    char pattern[] = "ABCDABD";
    bool result = is_substring(target, pattern);
    printf(result ? "true" : "false");
    return 0;
}