Use binary search to find interleaving sequence in C - c

Question

I have two arrays, A and X, where A >= X. I want to find the max interleaving factor i for X^i such that X^i is a subsequence of A. For example, if A = [4,3,2,1,4,3,2,1,4,3,2,1,4,3,2,1], and X = [1,2,3], then i = 1, because X^1 = [1,2,3] and that sequence is in A. My program should use a binary search to find this max interleaving factor i and trace whether or not each iteration is a sequence of A. So using binary search for the above example, i would start = 3 (as max possible for A/X = 6), and X^3 = [1,1,1,2,2,2,3,3,3] and that is not a sequence in A.
Here is my code so far:
#include <stdio.h>
#include <stdlib.h>
void create_initial_arrays(int size_a, int *A, int size_x, int *X);
void binary_search(int size_a, int * A, int size_x, int *X, int max_i, int min_i);
int main(){
int size_a, size_x;
scanf("%d", &size_a);
scanf("%d", &size_x);
int max_i = size_a / size_x;
int min_i = 0;
printf("Max: %d\n", max_i);
int *A = (int*) malloc(size_a *sizeof(int));
int *X = (int*) malloc(size_x *sizeof(int));
create_initial_arrays(size_a, A, size_x, X);
printf("Old X: ");
for(int i = 0; i < size_x; i++){
printf("%d ", X[i]);
}
printf("\n");
binary_search(size_a, A, size_x, X, max_i, min_i); //practice reallocating size of array
//for(int i = 0; i < size_x; i++){
// printf("%d ", A[i]);
//}
}
void create_initial_arrays(int size_a, int *A, int size_x, int *X){
int i, throwaway;
for(i = 0; i < size_a; i++){
scanf("%d", &A[i]);
}
scanf("%d", &throwaway);
for(i = 0; i < size_x; i++){
scanf("%d", &X[i]);
}
scanf("%d", &throwaway);
}
void binary_search(int size_a, int * A, int size_x, int *X, int max_i, int min_i){
int i, j, k, count = 0, max_repeat = 0;
while(min_i <= max_i){
int repeats = (max_i + min_i)/2;
printf("\n");
int * temp = realloc(X, size_x * sizeof(int) * repeats);
X = temp;
for(k = 0; k < size_x; ++k){
int idx = size_x - k -1;
temp = &X[idx];
for(j = 0; j < repeats; ++j){
X[idx * repeats + j] = *temp;
}
}
printf("New X: ");
for(i = 0; i < size_x * repeats; i++){
printf("%d ", X[i]);
}
for(i = 0; i < size_x * repeats; i++){
for(j = 0; j < size_a; j++){
if(A[j] == X[i]){
count++;
i++;
}
}
}
if (count == size_x * repeats){
printf("Low: %d Mid %d High % d Passes\n", min_i, repeats, max_i);
min_i = repeats + 1;
max_repeat++;
}
else
printf("Low: %d Mid %d High % d Fails\n", min_i, repeats, max_i);
max_i = repeats - 1;
}
printf("Max repeat: %d", max_repeat);
}
Here is my current output:
New X: 1 1 1 2 2 2 3 3 3 Low: 0 Mid 3 High 6 Fails
New X: 1 1 1 Low: 0 Mid 1 High 2 Fails
New X: Low: 0 Mid 0 High 0 Fails
I am expecting this:
New X: 1 1 1 2 2 2 3 3 3 Low: 0 Mid 3 High 6 Fails
New X: 1 2 3 Low: 0 Mid 1 High 2 Passes
New X: Low: 2 Mid 2 High 2 Fails
Max i = 1.
Meaning, that my code is not creating the correct array on the second iteration. X^1 should equal [1,2,3] not [1,1,1]. Why is it not creating the array properly on the second iteration but it does on the first?

Answer 1

Why is it not creating the array properly on the second iteration but it does on the first?
In the first loop you take X which is {1, 2, 3} and change it into {1, 1, 1, 2, 2, 2, 3, 3, 3} by repeating the first number 3 times, repeating the second number 3 times and repeating the third number 3 times.
In the second loop you start with X being {1, 1, 1, 2, 2, 2, 3, 3, 3}. Now you construct a new X by repeating the first number 1 time, repeating the second number 1 time and repeating the third number 1 time.
As the first, the second and the third numbers are all 1 you end up with {1, 1, 1}
In other words: Your first loop changed X and therefore you second loop use another value for X than the first loop. Consequently, the second loop produce an unexpected value for X