Dutch National Flag Algo

Python

def sort012(arr):
    low, mid, high = 0, 0, len(arr) - 1
    while mid <= high:
        if arr[mid] == 0:
            arr[low], arr[mid] = arr[mid], arr[low]
            low += 1
            mid += 1
        elif arr[mid] == 1:
            mid += 1
        else:
            arr[high], arr[mid] = arr[mid], arr[high]
            high += 1