Give Valid IP Addresses

backtracking/ip_address.py

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+"""
+    Restore IP Addresses
+    -> IP Address consists of exactly four integers seperated by single dots.
+    -> Each integer is between 0 and 255.
+    -> Exempli Gratia - 192.168.1.1 is valid ip address but 192.168@1.1 is an invalid ip address.
+
+    We are given with a string containing only digits , return all possible valid IP Addresses that 
+    can be formed by inserting dots in the string.
+    --> Not allowed to reorder or remove any digits in the string.
+    --> Return valid IP addresses in any order.
+
+    Topics covered: Backtracking
+
+    Example:
+    Input: s = "25525511135"
+    Output: ["255.255.11.135","255.255.111.35"]
+
+"""
+
+
+class Solution:
+    def restoreIpAddresses(self, s: str):
+        res = []
+
+        def backtrack(start, path):
+            # Base case: if we have 4 parts and used all digits
+            if len(path) == 4:
+                if start == len(s):
+                    res.append(".".join(path))
+                return
+
+            # Try segments of length 1 to 3
+            for l in range(1, 4):
+                if start + l > len(s):
+                    break
+                segment = s[start:start + l]
+
+                # Skip invalid parts (leading zeros or > 255)
+                if (segment.startswith('0') and len(segment) > 1) or int(segment) > 255:
+                    continue
+
+                backtrack(start + l, path + [segment])
+
+        backtrack(0, [])
+        return res