Equilibrium Index

equi.py

def equi ( A ):
    if len(A) < 1: return -1
    if len(A) == 1: return 0

    lsum = [0]
    rsum = [0]
    for i,a in enumerate(A):
        lsum.append(lsum[i] + a)
    lsum = lsum[:len(lsum)-1]

    for i,v in enumerate(reversed(A)):
        rsum.append(rsum[i] + v)
    rsum = rsum[:len(rsum)-1].reverse()

    for i,v in enumerate(A):
        if lsum[i] == rsum[i]:
            return i

    return -1