Short Problem Definition:
Find a symmetry point of a string, if any.
Link
Complexity:
expected worst-case time complexity is O(length(S))
expected worst-case space complexity is O(1) (not counting the storage required for input arguments).
Execution:
This problem gave me a lot of headache. It is so trivial I that over-complicated it. I thought that you should find a symmetry point at any possible position, ignoring the residual characters. You would obviously try to maximize the length of this symmetrical sub-array. I was not able to come with any O(S) algorithm for this problem derivation. So just to remind you, this problem is a simple palindrome check. Additionally, you drop all evenly sized strings as their symmetry point is between the indexes.
Solution:
def solution(S):
l = len(S)
if l % 2 == 0:
return -1
mid_point = l // 2
for idx in xrange(0, mid_point):
if S[idx] != S[l - idx - 1]:
return -1
return mid_point