添加 0017.电话号码的字母组合 python3版本

添加 0017.电话号码的字母组合 python3版本

problems/0017.电话号码的字母组合.md

@@ -272,7 +272,7 @@ class Solution {
         String str = numString[digits.charAt(num) - '0'];
         for (int i = 0; i < str.length(); i++) {
             temp.append(str.charAt(i));
-            //回溯
+            //c
             backTracking(digits, numString, num + 1);
             //剔除末尾的继续尝试
             temp.deleteCharAt(temp.length() - 1);
@@ -282,7 +282,25 @@ class Solution {
 ```
 
 Python：
-
+```python3
+class Solution:
+    def letterCombinations(self, digits: str) -> List[str]:
+        self.s = ""
+        res = []
+        letterMap = ["","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"]
+        if len(digits) == 0: return res
+        def backtrack(digits,index):
+            if index == len(digits):
+                return res.append(self.s)
+            digit = int(digits[index])  #将index指向的数字转为int
+            letters = letterMap[digit]  #取数字对应的字符集
+            for i in range(len(letters)):
+                self.s += letters[i]
+                backtrack(digits,index + 1)  #递归，注意index+1，一下层要处理下一个数字
+                self.s = self.s[:-1]  #回溯
+        backtrack(digits,0)
+        return res
+```
 
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