全排列

def solve():
    nums = [____, ____, ____]
    result = []
    def backtrack(____):
        if len(____) == len(____):
            result.append(____)
            return
        for i in range(len(____)):
            if not used[i]:
                used[i] = True
                path.append(____)
                backtrack(____)
                path.pop()
                used[i] = False
    backtrack([], [False] * len(____))
    print(____)