advent_of_code_2017_day_1_2

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

typedef struct {
    size_t size;
    size_t count;
    int *input_array;
} input_t;

input_t * initialize_input_struct();
int traverse_list(input_t *input, int current_pos);
void add_character(input_t *input, int input_data);
void read_input(input_t *input);
void parse_input(input_t *input);

int main() {
    input_t *input = initialize_input_struct();
    read_input(input);
    parse_input(input);
    return 0;
}

void parse_input(input_t *input) {
    // Keep track of the sum
    int sum = 0;
    // Keep track of the highest index
    int highest_index = input->count -1;
    // The increment is equal to the size of the list divided by two
    int increment = input->count / 2;
    // Keep track of the next index
    int next_index;

    // Loop through all the items
    for (int i = 0; i < input->count; ++i) {
        // Keep track of the current index
        int current_value = input->input_array[i];
        // If we can safely increment the index and proceed, do so
        if(i + increment <= highest_index) {
            next_index = i + increment;
        } else {
            // Check the number of steps you can safely take
            int valid_steps = highest_index - increment;
            // Proceed the number of steps and subtract them from the total distance to go
            int remaining_steps = increment - valid_steps;
            // Start from 0 and move forward the remaining number of steps
            next_index = remaining_steps - 1; // Subtract one to start from index 0
        }

        int next_value = input->input_array[next_index];
        // Check if the value in the current index is equal to the value in the next index
        if(current_value == next_value) {
            sum += current_value;
            printf("%i is equal to %i, sum: %i\n", current_value, next_value, sum);
        }
    }
}

void read_input(input_t *input) {
    FILE* f = fopen("input2.txt", "r");
    if(f) {
        while(!feof(f))  {
            char buffer;
            fscanf(f, "%c", &buffer);
            add_character(input, buffer - '0');
        }
    } else {
        printf("Failed to open file stream\n");
    }
    input->count -= 1; // When the list is complete, there is one unused space, remove this one
}

// Create an initial list with 10 elements
input_t * initialize_input_struct() {
    input_t *input = malloc(sizeof(input_t));
    input->size = 10;
    input->count = 0;
    input->input_array = malloc(sizeof(int) * input->size);
    return input;
}

// Add characters to the list 1 by 1
void add_character(input_t *input, int input_data) {
    if(input->size == input->count) {
        input->size += 10;
        input->input_array = realloc(input->input_array, sizeof(int) * input->size);
    }
    input->input_array[input->count] = input_data;
    input->count++;
}