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):
import sys

def make_pos(pos, S):
    N = len(S)
    for i in range(1, N-1):
        if pos[i] == 'S':
            if S[i] == 'o':
                pos[i+1] = pos[i-1]
            else:
                if pos[i-1] == 'S':
                    pos[i+1] = 'W'
                else:
                    pos[i+1] = 'S'

        else:
            if S[i] == 'o':
                if pos[i-1] == 'S':
                    pos[i+1] = 'W'
                else:
                    pos[i+1] = 'S'
            else:
                pos[i+1] = pos[i-1]

    if pos[0] == 'S':
        if S[0] == 'o':
            if pos[1] == pos[N-1]:
                return pos
            else:
                return False
        else:
            if pos[1] != pos[N-1]:
                return pos
            else:
                return False
    else:
        if S[0] == 'o':
            if pos[1] != pos[N-1]:
                return pos
            else:
                return False


def main():
    input = sys.stdin.readline
    N = int(input())
    S = str(input().strip())

    if S[0] == 'o':
        # Case 1 pos 0 is Sheep and neighbors are Wolves.
        pos = [0 for _ in range(N)]
        pos[0] = 'S'
        pos[1] = 'W'
        pos[N-1] = 'W'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 2: pos0 is Sheep ans neighbors are Sheeps.
        pos = [0 for _ in range(N)]
        pos[0] = 'S'
        pos[1] = 'S'
        pos[N-1] = 'S'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 3: pos0 is wolf and neibors are Sheep-Wolf.
        pos = [0 for _ in range(N)]
        pos[0] = 'W'
        pos[1] = 'S'
        pos[N-1] = 'W'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 4: pos0 is wolf and neibors are Wolf-Sheep.
        pos = [0 for _ in range(N)]
        pos[0] = 'W'
        pos[1] = 'W'
        pos[N-1] = 'S'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

    else:
        # Case 1 pos 0 is Sheep and neighbors are Sheep-Wolf.
        pos = [0 for _ in range(N)]
        pos[0] = 'S'
        pos[1] = 'S'
        pos[N-1] = 'W'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 2: pos0 is Sheep ans neighbors are Wolf-Sheep.
        pos = [0 for _ in range(N)]
        pos[0] = 'S'
        pos[1] = 'W'
        pos[N-1] = 'S'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 3: pos0 is wolf and neibors are Sheeps.
        pos = [0 for _ in range(N)]
        pos[0] = 'W'
        pos[1] = 'S'
        pos[N-1] = 'S'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

        # Case 4: pos0 is wolf and neibors are Wolves.
        pos = [0 for _ in range(N)]
        pos[0] = 'W'
        pos[1] = 'W'
        pos[N-1] = 'W'

        pos = make_pos(pos, S)
        if pos:
            return ''.join(pos)

    return -1


if __name__ == '__main__':
    print(main())


Fixed, accepted submission:
import sys

def check(pos, S, index):
    N = len(S)
    right = (index + 1) % N
    left = (index + (N - 1)) % N

    if pos[index] == 0:
        if S[index] == 'o':
            return pos[left] == pos[right]
        else:
            return pos[left] != pos[right]
    else:
        if S[index] == 'o':
            return pos[left] != pos[right]
        else:
            return pos[left] == pos[right]


def make_pos(pos, S):
    """Sheep: 0, Wolf: 1"""
    N = len(S)
    for i in range(1, N-1):
        if pos[i] == 0:
            if S[i] == 'o':
                pos[i+1] = pos[i-1]
            else:
                pos[i+1] = (pos[i-1] + 1) % 2

        else:
            if S[i] == 'o':
                pos[i+1] = (pos[i-1] + 1) % 2
            else:
                pos[i+1] = pos[i-1]

    if check(pos, S, 0) and check(pos, S, N-1):
        return pos
    else:
        return False


def main():
    input = sys.stdin.readline
    N = int(input())
    S = str(input().strip())

    
    pos = [-1 for _ in range(N)]
    pos[0] = 0
    pos[1] = 0
    pos = make_pos(pos, S)
    if pos:
        ans = ['S' if n == 0 else 'W' for n in pos]
        return ''.join(ans)

    
    pos = [-1 for _ in range(N)]
    pos[0] = 0
    pos[1] = 1
    pos = make_pos(pos, S)
    if pos:
        ans = ['S' if n == 0 else 'W' for n in pos]
        return ''.join(ans)

    
    pos = [-1 for _ in range(N)]
    pos[0] = 1
    pos[1] = 0
    pos = make_pos(pos, S)
    if pos:
        ans = ['S' if n == 0 else 'W' for n in pos]
        return ''.join(ans)

    
    pos = [-1 for _ in range(N)]
    pos[0] = 1
    pos[1] = 1
    pos = make_pos(pos, S)
    if pos:
        ans = ['S' if n == 0 else 'W' for n in pos]
        return ''.join(ans)

    return -1


if __name__ == '__main__':
    print(main())