recursive merge sort repetitive element print - recursion

Question

I am facing problem in the below code...
This code is of recursive merge sort but the array which gets printed has repetitive elements from the array.
help me in identifying the problem.
void merge(int arr[], int l, int mid, int h) {
int i = l;
int j = mid + 1;
int k = l;
int b[h + 1];
while (i <= mid && j <= h) {
if (arr[i] < arr[j])
b[k++] = arr[i++];
else
b[k++] = arr[j++];
}
while (i <= mid)
b[k++] = arr[i++];
while (j <= h)
b[k++] = arr[j++];
for (int i = 0; i <= h; i++)
arr[i] = b[i];
}
void Rmerge_sort(int arr[], int l, int h)
{
if (l < h) {
int mid = (h + l) / 2;
Rmerge_sort(arr, l, mid);
Rmerge_sort(arr, mid + 1, h);
merge(arr, l, mid, h);
}
}
int main() {
int arr[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 10 }, n = 10;
Rmerge_sort(arr, 0, n - 1);
for (int i = 0; i < n; i++)
cout << arr[i] << " ";
}

Answer 1

You define array b with size h + 1 instead of h - l + 1. The merge loops copy the elements to the index values l to h, but the final copy loop takes elements from 0 to h, copying elements from an uninitialized part.
Here is a corrected version:
void merge(int arr[], int l, int mid, int h) {
int len = h - l + 1;
int i = l;
int j = mid + 1;
int k = 0;
int b[len];
while (i <= mid && j <= h) {
if (arr[i] < arr[j])
b[k++] = arr[i++];
else
b[k++] = arr[j++];
}
while (i <= mid)
b[k++] = arr[i++];
while (j <= h)
b[k++] = arr[j++];
for (int i = 0; i < len; i++)
arr[l + i] = b[i];
}
Note however that a better approach to this problem is to save only the left half of the slice to merge and to consider h as the index of the first element after the end of the slice. This avoid confusing and error prone +1/-1 adjustments and reduces the number of copies:
void merge(int arr[], int low, int mid, int hi) {
int len1 = mid - lo;
int b[len1];
int i, j, k;
for (i = 0; i < len1; i++)
b[i] = a[low + i];
for (i = 0, j = mid, k = lo; i < len;) {
if (j >= hi || arr[i] <= arr[j])
arr[k++] = b[i++];
else
arr[k++] = arr[j++];
}
}
void Rmerge_sort(int arr[], int low, int hi) {
if (hi - low > 1) {
int mid = low + (hi - low) / 2; // avoid arithmetic overflow
Rmerge_sort(arr, low, mid);
Rmerge_sort(arr, mid, hi);
merge(arr, low, mid, hi);
}
}
int main() {
int arr[10] = { 9, 8, 7, 6, 5, 4, 3, 2, 1, 10 };
int n = sizeof(arr) / sizeof(arr[0]);
Rmerge_sort(arr, 0, n);
for (int i = 0; i < n; i++)
cout << arr[i] << " ";
}