949. Largest Time for Given Digits

sol.py

class Solution:
    
    def __init__(self):
        self.max_hours = -1
        self.max_minutes = -1
        
    def A_n_k_pythonic(self, a, used, curr, depth=0): # curr is the current solution
        if depth == 2:
            hours = curr[0] * 10 + curr[1]
            if hours < self.max_hours or hours > 23:
                return
            
        elif depth == len(a):
            hours = curr[0] * 10 + curr[1]
            minutes = curr[2] * 10 + curr[3]
            
            if hours > self.max_hours and minutes < 60:
                self.max_hours = hours
                self.max_minutes = minutes
            elif hours == self.max_hours and minutes < 60 and minutes > self.max_minutes:
                self.max_hours = hours
                self.max_minutes = minutes
                
            return
        
        for i in range(len(a)):
            if not used[i]:
                curr.append(a[i])
                used[i] = True
                self.A_n_k_pythonic(a, used, curr, depth + 1) # if the depth is 3 you only pop twice.
                curr.pop()
                used[i] = False
        return
    
    def largestTimeFromDigits(self, a: List[int]) -> str:
        used = [False] * len(a)
        self.A_n_k_pythonic(a, used, [])
        # print(self.max_hours, self.max_minutes)
        if self.max_hours == -1 or self.max_minutes == -1:
            return ""
        return "%02d:%02d" % (self.max_hours, self.max_minutes)