26. Merge Sort with Lower and Upper Bound Search.c

#include <stdio.h>
#include <stdlib.h>
void merge(int arr[], int l, int m, int r) {
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;

    int L[n1], R[n2];

    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];

    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) {
            arr[k] = L[i];
            i++;
        } else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}
    void mergeSort(int arr[], int l, int r) {
    if (l < r) {

        int m = l + (r - l) / 2;

        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);

        merge(arr, l, m, r);
    }
}

int lowerBound(int arr[], int n, int x) {
    int low = 0, high = n - 1, ans = -1;

    while (low <= high) {
        int mid = low + (high - low) / 2;

        if (arr[mid] <= x) {
            ans = mid;
            low = mid + 1;
        } else {
            high = mid - 1;
        }
    }

    return ans;
}

// Upper Bound
int upperBound(int arr[], int n, int x) {
    int low = 0, high = n - 1, ans = -1;

    while (low <= high) {
        int mid = low + (high - low) / 2;

        if (arr[mid] > x) {
            ans = mid;
            high = mid - 1;
        } else {
            low = mid + 1;
        }
    }

    return ans;
}

int main() {
    // Merge Sort
    int arr[] = {12, 11, 15, 1, 6, 7};
    int arr_size = sizeof(arr) / sizeof(arr[0]);

    printf("Given array is \n");
    for (int i = 0; i < arr_size; i++)
        printf("%d ", arr[i]);

    // Perform merge sort
    mergeSort(arr, 0, arr_size - 1);

    printf("\nSorted array is \n");
    for (int i = 0; i < arr_size; i++)
        printf("%d ", arr[i]);

    // Lower and Upper Bounds
    int x = 10;

    int lowerIndex = lowerBound(arr, arr_size, x);
    int upperIndex = upperBound(arr, arr_size, x);

    printf("\nLower bound of %d is at index: %d and value: %d\n", x, lowerIndex, (lowerIndex != -1) ? arr[lowerIndex] : -1);
    printf("Upper bound of %d is at index: %d and value: %d\n", x, upperIndex, (upperIndex != -1) ? arr[upperIndex] : -1);

    return 0;
}