QuickSort - Partitioning

Lomuto partition rearranges around pivot: $1.$ Choose last as pivot.

$2.$ Index $i$ tracks boundary of $<$ pivot.

$3.$ Scan with $j$. If $arr[j] < pivot$, swap with $arr[i+1]$, increment $i$.

$4.$ Swap pivot to $i+1$.

function partition(arr, low, high):
    pivot = arr[high]
    i = low - 1
    for j from low to high-1:
        if arr[j] < pivot:
            i++; swap(arr[i], arr[j])
    swap(arr[i+1], arr[high])
    return i + 1

Pivot ends at final sorted position.