Assignment-1/ass1.c

/* License: AGPLv3 or later. https://www.gnu.org/licenses/licenses.html
 * 
 * Assignment 1 - Text Analysis
 * Manish
 * Student Login: *****
 * 
 * Compile it as:
 * gcc -Wall -std=c11 -o ass1 ass1.c
 * 
 * Relevant code has been carried over from Lab Exercises
 * 
 * Word are ordered by decreasing count and than alphabetically in
 * ascending order. Eg:
 * 15 hello
 * 15 world
 */

#include <ctype.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct
{
    // Word
    int start;
    /* Not required as next node's start -1 is end.
     * For last word, it's text_size -1.
     */
    // int end;
    int count;

    // AVL tree
    int left;
    int right;
    int height;
} node;

// This is the AVL tree
int root = -1;
node tree[50000];
int tree_size = 0;

// All words in string pool. Their index in AVL tree
char text[500000];
int text_size = 0;

/* Alphabetical index is built by traversing through tree.
 * Thereafter, sort indexes by count using merge sort.
 */
int indexes[50000];
int indexes_size = 0;

int min(int i, int j);
int max(int i, int j);

int string_compare(int node_i, int index_j);
int new_entry(int start);
int height(int node);
void update_hegiht(int node);
int insert(int start, int node);
int rotate_right(int old_parent);
int rotate_left(int old_parent);
void build_index(int node_index);

void merge_sort();

void print_word(int node);

int main(void)
{
    printf("Enter file name: ");
    char filename[257];
    // Assuming filename/file path won't be longer than 256 characters
    scanf("%256s", filename);

    FILE* file = fopen(filename, "r");
    if (!file)
    {
        perror(filename);
        exit(EXIT_FAILURE);
    }

    // read word and add node to AVL tree
    int word_start = text_size;
    int tree_len = tree_size;
    char c;
    bool in_word = false;
    while ((c = fgetc(file)) != EOF)
    {
        if (isalpha(c))
        {
            if (!in_word)
            {
                in_word = true;
                word_start = text_size;
            }
            text[text_size++] = tolower(c);
        }
        else if (isspace(c))
        {
            if (in_word)
            {
                root = insert(word_start, root);
                // if word not added because duplicate
                if (tree_len == tree_size)
                {
                    text_size = word_start;
                }
                else
                {
                    tree_len = tree_size;
                }
            }
            in_word = false;
        }
    }

    fclose(file);

    build_index(root);

    merge_sort();

    printf("First 10 words in index:\n");
    int upto = min(indexes_size, 10);
    for (int i = 0; i < upto; i++)
    {
        print_word(indexes[i]);
    }
    printf("\n\nLast 10 words in index:\n");
    int from = max(indexes_size - 11, 0);
    for (int i = from; i < indexes_size; i++)
    {
        print_word(indexes[i]);
    }

    return 0;
}

int min(int i, int j)
{
    if (i <= j)
        return i;
    return j;
}

int max(int i, int j)
{
    if (i >= j)
        return i;
    return j;
}

/* node_i is a word added to tree and index_j is last word in
 * text that needs to be compared.
 */
int string_compare(int node_i, int index_j)
{
    /* If alphabetically node_i comes before than -1
     * if node_i == index_j than 0
     * if alphabetically nojde_j comes before than 1
     */
    int i = tree[node_i].start;
    int j = index_j;
    int i_end;
    if (node_i + 1 == tree_size) // node_i is last entry
        i_end = index_j;
    else
        i_end = tree[node_i + 1].start; // start of next word in text array
    int j_end = text_size;
    while (i < i_end && j < j_end)
    {
        if (text[i] < text[j])
            return -1;
        if (text[i++] > text[j++])
            return 1;
    }
    // till now both are equal
    if (i < i_end) // i is longer
        return 1;
    if (j < j_end) // j is longer
        return -1;
    return 0; // Both equal and same length
}

int new_entry(int word_start)
{
    tree[tree_size].start = word_start;
    tree[tree_size].count = 1;
    tree[tree_size].left = -1;
    tree[tree_size].right = -1;
    tree[tree_size].height = 0;
    return tree_size++;
}

int height(int node)
{
    if (node >= 0)
    {
        return tree[node].height;
    }
    return node; // -1
}

void update_hegiht(int node)
{
    int left_height = height(tree[node].left);
    int right_height = height(tree[node].right);
    tree[node].height = max(left_height, right_height) + 1;
}

int insert(int word_start, int node)
{
    if (node < 0)
    {
        return new_entry(word_start);
    }
    int comparison = string_compare(node, word_start);
    // new_word == our_word
    if (comparison == 0)
        tree[node].count++;
    // new_word < our_word
    else if (comparison > 0)
    {
        tree[node].left = insert(word_start, tree[node].left);
        // if tree imbalance
        if (height(tree[node].left) - height(tree[node].right) >= 2)
        {
            if (string_compare(tree[node].left, word_start) > 0) // Case 1
            {
                node = rotate_right(node);
            }
            else // Case 2
            {
                tree[node].left = rotate_left(tree[node].left);
                node = rotate_right(node);
            }
        }
    }
    // new_word > our_word
    else if (comparison < 0)
    {
        tree[node].right = insert(word_start, tree[node].right);
        // if tree imbalance
        if (height(tree[node].right) - height(tree[node].left) >= 2)
        {
            if (string_compare(tree[node].right, word_start) > 0) // Case 3
            {
                tree[node].right = rotate_right(tree[node].right);
                node = rotate_left(node);
            }
            else // Case 4
            {
                node = rotate_left(node);
            }
        }
    }
    update_hegiht(node);
    return node;
}

int rotate_right(int old_parent)
{
    int new_parent = tree[old_parent].left;
    tree[old_parent].left = tree[new_parent].right;
    tree[new_parent].right = old_parent;
    update_hegiht(old_parent);
    update_hegiht(new_parent);
    return new_parent; // to be updated in it's grand parent node
}

int rotate_left(int old_parent)
{
    int new_parent = tree[old_parent].right;
    tree[old_parent].right = tree[new_parent].left;
    tree[new_parent].left = old_parent;
    update_hegiht(old_parent);
    update_hegiht(new_parent);
    return new_parent; // to be updated in it's grand parent node
}

void build_index(int node)
{
    if (node < 0)
        return;
    build_index(tree[node].left);
    indexes[indexes_size++] = node;
    build_index(tree[node].right);
}

void merge_sort()
{
    int temp[indexes_size];

    // These pointers will be swapped at every iteration
    int* src = indexes;
    int* dst = temp;
    int* tmp;

    int merge_size = 1;
    // It looks O(scary!) but is as efficient as other loop based merge sort
    while (merge_size < indexes_size)
    {
        int i = 0;
        while (i < indexes_size)
        {
            int left_upto = min(i + merge_size, indexes_size);
            int l = i;
            int r = left_upto;
            int right_upto = min(i + (2 * merge_size), indexes_size);
            while (l < left_upto && r < right_upto)
            {
                if (tree[src[l]].count >= tree[src[r]].count)
                {
                    dst[i++] = src[l++];
                }
                else
                {
                    dst[i++] = src[r++];
                }
            }
            for (; l < left_upto; l++)
            {
                dst[i++] = src[l];
            }
            for (; r < right_upto; r++)
            {
                dst[i++] = src[r];
            }
        }
        tmp = src;
        src = dst;
        dst = tmp;
        merge_size *= 2;
    }
    /* if loop ended with final merge in temp array than copy it back to
     * indexes array
     */
    if (&indexes[0] != &src[0])
    {
        for (int i = 0; i < indexes_size; i++)
        {
            indexes[i] = src[i];
        }
    }
}

void print_word(int node)
{
    int word_length;
    if (node + 1 == tree_size) // last word in tree
        word_length = text_size - tree[node].start;
    else
        word_length = tree[node + 1].start - tree[node].start;
    printf(
        "%d %.*s\n",
        tree[node].count,
        word_length,
        &text[tree[node].start]);
}