TalentBuddy.co Tuple Sum using DFS

tuple_sum.py

def tuple_sum(a, s):
    ret = backtrack(a, s, 0, 1, 2, 3)
    print ' '.join(str(i) for i in ret)

def backtrack(a, s, x, y, w, z):
    result = a[x] + a[y] + a[w] + a[z]
    
    conj = set([x, y, w, z])
       
    if result == s and len(conj) == 4:
        return (x, y, w, z)      
    
    aux = None
    
    if (z + 1) < len(a):
        aux = backtrack(a, s, x, y, w, z + 1)
    
    if not aux is None:
        return aux
    
    if (w + 1) < len(a):
        aux = backtrack(a, s, x, y, w + 1, z)
        
    if not aux is None:
        return aux
    
    if (y + 1) < len(a):
        aux = backtrack(a, s, x, y + 1, w, z)
    
    if not aux is None:
        return aux
    
    if (x + 1) < len(a):
        aux = backtrack(a, s, x + 1, y, w, z)
        
    if not aux is None:
        return aux
    
    return None