def merge_sort(arr):
    """
    Merge Sort - O(n log n) time complexity
    Divide and conquer algorithm that divides array into halves, sorts them and merges.
    """
    if len(arr) <= 1:
        return arr
    
    mid = len(arr) // 2
    left = merge_sort(arr[:mid])
    right = merge_sort(arr[mid:])
    
    return merge(left, right)

def merge(left, right):
    result = []
    i = j = 0
    
    while i < len(left) and j < len(right):
        if left[i] <= right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1
    
    result.extend(left[i:])
    result.extend(right[j:])
    return result

# Example usage
data = [64, 34, 25, 12, 22, 11, 90]
print("Original:", data)
print("Sorted:", merge_sort(data))