3 pointer sort

class :
    """
    @param nums: A list of integer which is 0, 1 or 2 
    @return: nothing
    """
    def sortColors(self, a):
        
        pl, pr = 0, len(a)-1
        i = 0
        while i <= pr:
            if a[i] == 0:
                a[pl], a[i] = a[i], a[pl]
                i+=1
                pl+=1
            elif a[i] == 1:
                i += 1
            else:
                a[pr], a[i] = a[i], a[pr] 
                pr-=1