Merge sort algorithm is not functioning properly

Question

A merge sorting algorithm is not working as it is supposed to do. The output values are not fully sorted in the ascending order. Some of the values are out of order which is pointing to a bug.

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

void merge(int *L, int *R, int *a, int nL, int nR) {
    int i, j, k;
    i = j = k = 0;

    while ((i < nL) && (j < nL)) {
        if (L[i] < R[j]) {
            a[k] = L[i];
            ++i;
        } else {
            a[k] = R[j];
            ++j;
        }
        ++k;
    }

    while (i < nL) {
        a[k] = L[i];
        ++i;
        ++k;
    }

    while (j < nR) {
        a[k] = R[j];
        ++j;
        ++k;
    }
}

void mergeSort(int *a, int n) {
    if (n < 2)
        return;

    int i, mid, *L, *R;

    mid = n / 2;

    L = (int *)malloc(mid * sizeof(int));
    R = (int *)malloc((n - mid) * sizeof(int));

    for (i = 0; i < mid; ++i) {
        L[i] = a[i];
    }

    for (i = mid; i < n; ++i) {
        R[i - mid] = a[i];
    }

    mergeSort(L, mid);
    mergeSort(R, n - mid);

    merge(L, R, a, mid, n - mid);

    free(L);
    free(R);
}

int main() {
    int i, n, *a;

    scanf("%d", &n);

    a = (int *)malloc(n * sizeof(int));

    for (i = 0; i < n; ++i) {
        scanf("%d", &a[i]);
    }

    mergeSort(a, n);

    for (i = 0; i < n; ++i) {
        printf("%d ", a[i]);
    }

    free(a);

    return 0;
}

For example, for the following inputs: 10 10 9 8 7 6 5 4 3 2 1

I should get these outputs: 1 2 3 4 5 6 7 8 9 10

But the outputs are not in the ascending order. The outputs are:1 3 4 5 2 6 8 9 10 7

Answer 1

Not sure if it covers all the problems but

while((i < nL) && (j < nL))

should be

while((i < nL) && (j < nR))
                        ^
                        note