Update 0093.复原IP地址.md

problems/0093.复原IP地址.md

@@ -360,104 +360,82 @@ class Solution {
 
 ## python
 
-python2:
-```python
-class Solution(object):
-    def restoreIpAddresses(self, s):
-        """
-        :type s: str
-        :rtype: List[str]
-        """
-        ans = []
-        path = []
-        def backtrack(path, startIndex):
-            if len(s) > 12: return []
-            if len(path) == 4:
-                if startIndex == len(s):
-                    ans.append(".".join(path[:]))
-                    return
-            for i in range(startIndex+1, min(startIndex+4, len(s)+1)):  # 剪枝
-                string = s[startIndex:i]
-                if not 0 <= int(string) <= 255:
-                    continue
-                if not string == "0" and not string.lstrip('0') == string:
-                    continue
-                path.append(string)
-                backtrack(path, i)
-                path.pop()
-
-        backtrack([], 0)
-        return ans
-```
-
-python3:
+回溯（版本一）
 ```python
 class Solution:
-    def __init__(self):
-        self.result = []
-
     def restoreIpAddresses(self, s: str) -> List[str]:
-        '''
-        本质切割问题使用回溯搜索法，本题只能切割三次，所以纵向递归总共四层
-        因为不能重复分割，所以需要start_index来记录下一层递归分割的起始位置
-        添加变量point_num来记录逗号的数量[0,3]
-        '''
-        self.result.clear()
-        if len(s) > 12: return []
-        self.backtracking(s, 0, 0)
-        return self.result
+        result = []
+        self.backtracking(s, 0, 0, "", result)
+        return result
 
-    def backtracking(self, s: str, start_index: int, point_num: int) -> None:
-        # Base Case
-        if point_num == 3:
-            if self.is_valid(s, start_index, len(s)-1):
-                self.result.append(s[:])
+    def backtracking(self, s, start_index, point_num, current, result):
+        if point_num == 3:  # 逗点数量为3时，分隔结束
+            if self.is_valid(s, start_index, len(s) - 1):  # 判断第四段子字符串是否合法
+                current += s[start_index:]  # 添加最后一段子字符串
+                result.append(current)
             return
-        # 单层递归逻辑
-        for i in range(start_index, len(s)):
-            # [start_index, i]就是被截取的子串
-            if self.is_valid(s, start_index, i):
-                s = s[:i+1] + '.' + s[i+1:]
-                self.backtracking(s, i+2, point_num+1)  # 在填入.后，下一子串起始后移2位
-                s = s[:i+1] + s[i+2:]    # 回溯
-            else:
-                # 若当前被截取的子串大于255或者大于三位数，直接结束本层循环
-                break
-    
-    def is_valid(self, s: str, start: int, end: int) -> bool:
-        if start > end: return False
-        # 若数字是0开头，不合法
-        if s[start] == '0' and start != end:
-            return False
-        if not 0 <= int(s[start:end+1]) <= 255:
-            return False
-        return True
-```
 
-python3; 简单拼接版本（类似Leetcode131写法）：
+        for i in range(start_index, len(s)):
+            if self.is_valid(s, start_index, i):  # 判断 [start_index, i] 这个区间的子串是否合法
+                sub = s[start_index:i + 1]
+                self.backtracking(s, i + 1, point_num + 1, current + sub + '.', result)
+            else:
+                break
+
+    def is_valid(self, s, start, end):
+        if start > end:
+            return False
+        if s[start] == '0' and start != end:  # 0开头的数字不合法
+            return False
+        num = 0
+        for i in range(start, end + 1):
+            if not s[i].isdigit():  # 遇到非数字字符不合法
+                return False
+            num = num * 10 + int(s[i])
+            if num > 255:  # 如果大于255了不合法
+                return False
+        return True
+
+```
+回溯（版本二）
+
 ```python
-class Solution: 
+class Solution:
     def restoreIpAddresses(self, s: str) -> List[str]:
-        global results, path
         results = []
-        path = []
-        self.backtracking(s,0)
+        self.backtracking(s, 0, [], results)
         return results
 
-    def backtracking(self,s,index):
-        global results,path
-        if index == len(s) and len(path)==4:
-            results.append('.'.join(path)) # 在连接时需要中间间隔符号的话就在''中间写上对应的间隔符
+    def backtracking(self, s, index, path, results):
+        if index == len(s) and len(path) == 4:
+            results.append('.'.join(path))
             return
-        for i in range(index,len(s)):
-            if len(path)>3: break          # 剪枝
-            temp = s[index:i+1]
-            if (int(temp)<256 and int(temp)>0 and temp[0]!='0') or (temp=='0'):
-                path.append(temp)
-                self.backtracking(s,i+1)
-                path.pop()      
+
+        if len(path) > 4:  # 剪枝
+            return
+
+        for i in range(index, min(index + 3, len(s))):
+            if self.is_valid(s, index, i):
+                sub = s[index:i+1]
+                path.append(sub)
+                self.backtracking(s, i+1, path, results)
+                path.pop()
+
+    def is_valid(self, s, start, end):
+        if start > end:
+            return False
+        if s[start] == '0' and start != end:  # 0开头的数字不合法
+            return False
+        num = int(s[start:end+1])
+        return 0 <= num <= 255
+
+
+
+
 ```
 
+
+
 ## Go 
 
 ```go