from functools import reduce
import math

def listtotal(xs):
    if len(xs) == 0:
        return 0
    else:
        return reduce(lambda x,y: x + y, xs)

def reversecopy(xs):
    output = []
    for i in xs:
        output.insert(0,i)
    return output

def pilesort(n,p,s): #splits [1,n] into p subsets, each summing to s.
    output = []
    numbers = list(range(1,n+1))
    templist = []
    if (s*p) == int(n*(n+1)/2): #if it even makes sense to try doing this
        while len(output) < p:
            templist = []
            while not listtotal(templist) == s:
                for i in reversecopy(list(range(0,len(numbers)))):
                    if listtotal(templist) + numbers[i] <= s:
                        templist.append(numbers.pop(i))
            output.append(templist)
    else:
        return "Error!"
    return output