LAIB 8 Exercise 2: Gray Code

laib8ex2.c

#include <stdio.h>
#include <stdlib.h>

char s[]={'0','1'};

int power(int b, int e){
    return e!=0?b*power(b,e-1):1;
}

void gray_r(char **matrix,int n,int shift,int symbol){
    if(n==0)return;
    int i,half=power(2,n)/2;
    for(i=0;i<half;i++)matrix[0][shift+i]=s[symbol];
    for(i=0;i<half;i++)matrix[0][shift+i+half]=s[!symbol];
    gray_r(&matrix[1],n-1,shift,symbol);
    gray_r(&matrix[1],n-1,shift+half,!symbol);
}

char **makeGray(int n){
    int i;
    char **gray_matrix=(char **)malloc(n*sizeof(char*));
    if(gray_matrix==NULL)return NULL;
    for(i=0;i<n;i++){
        gray_matrix[i]=(char*)malloc((power(2,n)+1)*sizeof(char));
        if(gray_matrix[i]==NULL){
            while(i>0)free(gray_matrix[--i]);
            free(gray_matrix);
            return NULL;
        }
        gray_matrix[i][power(2,n)]='\0';//Too lazy to print one by one
    }
    gray_r(gray_matrix,n,0,0);
    return gray_matrix;
}

void printGray(char **gray_matrix,int n){
    int i;
    for(i=0;i<n;i++)printf("%s\n",gray_matrix[i]);
}

int main(int argc, char **argv){
    char **gray_matrix;
    int i;

    if(argc<2){
        printf("ERROR: Wrong number of arguments, 1 integer needed.\n");
        return EXIT_FAILURE;
    }

    int n=atoi(argv[1]);

    gray_matrix=makeGray(n);
    if(gray_matrix==NULL){
        printf("Something dark(er) happened...\n");
        return EXIT_FAILURE;
    }

    printGray(gray_matrix,n);

    for(i=0;i<n;i++)free(gray_matrix[i]);
    free(gray_matrix);

    return 0;
}