From 847c60ac3c93af41eaba8bf8e48de71c5eb728ab Mon Sep 17 00:00:00 2001 From: jianghongcheng <35664721+jianghongcheng@users.noreply.github.com> Date: Fri, 26 May 2023 06:41:01 -0500 Subject: [PATCH] =?UTF-8?q?Update=200017.=E7=94=B5=E8=AF=9D=E5=8F=B7?= =?UTF-8?q?=E7=A0=81=E7=9A=84=E5=AD=97=E6=AF=8D=E7=BB=84=E5=90=88.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0017.电话号码的字母组合.md | 207 ++++++++++++------- 1 file changed, 131 insertions(+), 76 deletions(-) diff --git a/problems/0017.电话号码的字母组合.md b/problems/0017.电话号码的字母组合.md index d1135497..9f1473db 100644 --- a/problems/0017.电话号码的字母组合.md +++ b/problems/0017.电话号码的字母组合.md @@ -285,98 +285,153 @@ class Solution { ``` ## Python -**回溯** +回溯 ```python class Solution: def __init__(self): - self.answers: List[str] = [] - self.answer: str = '' - self.letter_map = { - '2': 'abc', - '3': 'def', - '4': 'ghi', - '5': 'jkl', - '6': 'mno', - '7': 'pqrs', - '8': 'tuv', - '9': 'wxyz' - } - - def letterCombinations(self, digits: str) -> List[str]: - self.answers.clear() - if not digits: return [] + self.letterMap = [ + "", # 0 + "", # 1 + "abc", # 2 + "def", # 3 + "ghi", # 4 + "jkl", # 5 + "mno", # 6 + "pqrs", # 7 + "tuv", # 8 + "wxyz" # 9 + ] + self.result = [] + self.s = "" + + def backtracking(self, digits, index): + if index == len(digits): + self.result.append(self.s) + return + digit = int(digits[index]) # 将索引处的数字转换为整数 + letters = self.letterMap[digit] # 获取对应的字符集 + for i in range(len(letters)): + self.s += letters[i] # 处理字符 + self.backtracking(digits, index + 1) # 递归调用，注意索引加1，处理下一个数字 + self.s = self.s[:-1] # 回溯，删除最后添加的字符 + + def letterCombinations(self, digits): + if len(digits) == 0: + return self.result self.backtracking(digits, 0) - return self.answers - - def backtracking(self, digits: str, index: int) -> None: - # 回溯函数没有返回值 - # Base Case - if index == len(digits): # 当遍历穷尽后的下一层时 - self.answers.append(self.answer) - return - # 单层递归逻辑 - letters: str = self.letter_map[digits[index]] - for letter in letters: - self.answer += letter # 处理 - self.backtracking(digits, index + 1) # 递归至下一层 - self.answer = self.answer[:-1] # 回溯 + return self.result + ``` -**回溯简化** +回溯精简（版本一） ```python class Solution: def __init__(self): - self.answers: List[str] = [] - self.letter_map = { - '2': 'abc', - '3': 'def', - '4': 'ghi', - '5': 'jkl', - '6': 'mno', - '7': 'pqrs', - '8': 'tuv', - '9': 'wxyz' - } - - def letterCombinations(self, digits: str) -> List[str]: - self.answers.clear() - if not digits: return [] - self.backtracking(digits, 0, '') - return self.answers + self.letterMap = [ + "", # 0 + "", # 1 + "abc", # 2 + "def", # 3 + "ghi", # 4 + "jkl", # 5 + "mno", # 6 + "pqrs", # 7 + "tuv", # 8 + "wxyz" # 9 + ] + self.result = [] - def backtracking(self, digits: str, index: int, answer: str) -> None: - # 回溯函数没有返回值 - # Base Case - if index == len(digits): # 当遍历穷尽后的下一层时 - self.answers.append(answer) - return - # 单层递归逻辑 - letters: str = self.letter_map[digits[index]] + def getCombinations(self, digits, index, s): + if index == len(digits): + self.result.append(s) + return + digit = int(digits[index]) + letters = self.letterMap[digit] for letter in letters: - self.backtracking(digits, index + 1, answer + letter) # 递归至下一层 + 回溯 + self.getCombinations(digits, index + 1, s + letter) + + def letterCombinations(self, digits): + if len(digits) == 0: + return self.result + self.getCombinations(digits, 0, "") + return self.result + ``` -**使用itertools** +回溯精简（版本二） ```python class Solution: - def letterCombinations(self, digits: str) -> List[str]: - import itertools - if not digits: - return list() - - phoneMap = { - "2": "abc", - "3": "def", - "4": "ghi", - "5": "jkl", - "6": "mno", - "7": "pqrs", - "8": "tuv", - "9": "wxyz", - } + def __init__(self): + self.letterMap = [ + "", # 0 + "", # 1 + "abc", # 2 + "def", # 3 + "ghi", # 4 + "jkl", # 5 + "mno", # 6 + "pqrs", # 7 + "tuv", # 8 + "wxyz" # 9 + ] + + def getCombinations(self, digits, index, s, result): + if index == len(digits): + result.append(s) + return + digit = int(digits[index]) + letters = self.letterMap[digit] + for letter in letters: + self.getCombinations(digits, index + 1, s + letter, result) + + def letterCombinations(self, digits): + result = [] + if len(digits) == 0: + return result + self.getCombinations(digits, 0, "", result) + return result + - groups = (phoneMap[digit] for digit in digits) - return ["".join(combination) for combination in itertools.product(*groups)] ``` +回溯优化使用列表 +```python +class Solution: + def __init__(self): + self.letterMap = [ + "", # 0 + "", # 1 + "abc", # 2 + "def", # 3 + "ghi", # 4 + "jkl", # 5 + "mno", # 6 + "pqrs", # 7 + "tuv", # 8 + "wxyz" # 9 + ] + + def getCombinations(self, digits, index, path, result): + if index == len(digits): + result.append(''.join(path)) + return + digit = int(digits[index]) + letters = self.letterMap[digit] + for letter in letters: + path.append(letter) + self.getCombinations(digits, index + 1, path, result) + path.pop() + + def letterCombinations(self, digits): + result = [] + if len(digits) == 0: + return result + self.getCombinations(digits, 0, [], result) + return result + + + +``` + + ## Go