equi2.py

tests = [
    ([-7, 1, 5, 2, -4, 3, 0], [3,6]),
    ([1, 2, 3, 4, 3, 2, 1], [3]),
    ([99, 0, 66, 32, 1] , [1]),
    ([1, -1, 1, -1, 1, -1, 1], [0,1,2,3,4,5,6]),
    ([0,0,0], [0,1,2]),
    ([0,53,9], -1),
    ([0,1,-1], [0]),
    ([-1, 0, 1], -1),
]
 
def equi(A):
    s = [] # list of eq. indices
 
    for i in range(len(A)):
        if sum(A[:i]) == sum(A[i+1:]):
            s.append(i)
    if s:    
        return s
    else:
        return -1  

def fast_equi(A):
    l = 0 # left of current index
    r = sum(A) # right of current index
    s = [] # list of eq. indices
 
    for i in range(len(A)):
        r -= A[i]
        if l == r:
            s.append(i)
        l += A[i]
    if s:    
        return s
    else:
        return -1  
 
if __name__ == "__main__":
    for (i, r) in tests:
        if r != equi(i):
            print r, "!=", equi(i), "for", i
        if r != fast_equi(i):
            print r, "!=", fast_equi(i), "for", i, "(fast)"