[leetcode---dfs]电话号码的字母组合

一是第一次熟悉python的类的写法
二是这个有好多循环，有点绕

class Solution:        
    def letterCombinations_sub(self, num:list, dig:list, p:list,cur:str, n:int)-> List[str]:
        if(n < len(num) - 1):
            for i in range(len(dig[num[n]])):
                p = self.letterCombinations_sub(num, dig, p, cur + dig[num[n]][i], n+1)
        else:'''长度达到len(num) - 1, 等于构造好了'''
            for i in range(len(dig[num[n]])):
                p.append(cur+dig[num[n]][i])
        return p
        
    def letterCombinations(self, digits: str) -> List[str]:  
        dig = [[] for _ in range(8)]
        num = []    
        p = []
        n = 0
        if(len(digits) == 0):
            return []
        for i in range(5):
            st = ord("a") + i * 3
            dig[i].append(chr(st))
            dig[i].append(chr(st+1))
            dig[i].append(chr(st+2))
        dig[5].extend(['p','q','r','s'])
        dig[6].extend(['t','u','v'])
        dig[7].extend(['w','x','y','z'])
        for i in range(len(digits)):
            num.append(int(digits[i]) - 2)
        cur = ""
        return self.letterCombinations_sub(num, dig,p,cur,n)