문제 링크

정답 :

def solution(arr):
    answer = []
    
    for idx, i in enumerate(arr):
        if len(answer) == 0:
            answer.append(i)
        elif answer[-1] == i:
            answer.pop()
        elif answer[-1] != i:
            answer.append(i)
    
    return answer if answer else [-1]

방법 1.

def solution(arr):
    stk = []
    for i in range(len(arr)):
        if stk and stk[-1] == arr[i]:
            stk.pop()
        else:
            stk.append(arr[i])

    return stk or [-1]