Problem:
Snuke, who loves animals, built a zoo.  There are N animals in this zoo. They are conveniently numbered 1 through N, and arranged in a circle. The animal numbered i (2≤i≤N-1) is adjacent to the animals numbered i-1 and i+1. Also, the animal numbered 1 is adjacent to the animals numbered 2 and N, and the animal numbered N is adjacent to the animals numbered N-1 and 1.  There are two kinds of animals in this zoo: honest sheep that only speak the truth, and lying wolves that only tell lies.  Snuke cannot tell the difference between these two species, and asked each animal the following question: "Are your neighbors of the same species?" The animal numbered i answered s_i. Here, if s_i is `o`, the animal said that the two neighboring animals are of the same species, and if s_i is `x`, the animal said that the two neighboring animals are of different species.  More formally, a sheep answered `o` if the two neighboring animals are both sheep or both wolves, and answered `x` otherwise. Similarly, a wolf answered `x` if the two neighboring animals are both sheep or both wolves, and answered `o` otherwise.  Snuke is wondering whether there is a valid assignment of species to the animals that is consistent with these responses. If there is such an assignment, show one such assignment. Otherwise, print `-1`.

Incorrect submission (verdict: Wrong Answer):
from collections import defaultdict


def ok(l, s):
    for i in range(len(s) * 2):
        now = i % len(l)
        pre = now - 1
        nex = (now + 1) % len(l)
        if (l[now] == -1 and s[now] == 'x') or (l[now] == 1 and s[now] == 'o'):
            if l[nex] is None:
                l[nex] = l[pre]
            else:
                if l[nex] != l[pre]:
                    return False
        else:
            if l[nex] is None:
                l[nex] = -1 * l[pre]
            else:
                if l[nex] != -1 * l[pre]:
                    return False

    return True


def main():
    N = int(input())
    s = input()

    for x in [(-1, -1), (-1, 1), (1, -1), (1, 1)]:
        l = [None] * N
        l[-1], l[0] = x[0], x[1]
        if ok(l, s):
            print("".join(['w' if x == -1 else 's' for x in l]))
            return
    print(-1)


if __name__ == '__main__':
    main()


Fixed, accepted submission:
from collections import defaultdict, Counter
from itertools import product, groupby, count, permutations, combinations
from math import pi, sqrt
from collections import deque
from bisect import bisect, bisect_left, bisect_right
from string import ascii_lowercase
from functools import lru_cache
import sys
sys.setrecursionlimit(10000)
INF = float("inf")
YES, Yes, yes, NO, No, no = "YES", "Yes", "yes", "NO", "No", "no"
dy4, dx4 = [0, 1, 0, -1], [1, 0, -1, 0]
dy8, dx8 = [0, -1, 0, 1, 1, -1, -1, 1], [1, 0, -1, 0, 1, 1, -1, -1]


def inside(y, x, H, W):
    return 0 <= y < H and 0 <= x < W


def ceil(a, b):
    return (a + b - 1) // b


def ok(last, first, S):
    N = len(S)
    ans = [None] * N
    ans[-1], ans[0] = last, first

    for i in range(N):

        if ans[i] == 0:
            if S[i] == "o":
                nex = ans[i - 1]
            else:
                nex = 1 - ans[i - 1]
        else:
            if S[i] == "o":
                nex = 1 - ans[i - 1]
            else:
                nex = ans[i - 1]

        if ans[(i + 1) % N] is None:
            ans[(i + 1) % N] = nex
        else:
            if ans[(i + 1) % N] != nex:
                return None
    return ans


def main():
    N = int(input())
    S = input()

    for l, f in [(0, 0), (0, 1), (1, 0), (1, 1)]:
        ans = ok(l, f, S)
        if ans is not None:
            print(*["S" if v == 0 else "W" for v in ans], sep="")
            return
    print(-1)


if __name__ == '__main__':
    main()