Added restore_ip_addresses

Author: shichao-an

restore_ip_addresses/solution.py

@@ -0,0 +1,48 @@
+"""
+Given a string containing only digits, restore it by returning all possible
+valid IP address combinations.
+
+For example:
+Given "25525511135",
+
+return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)
+"""
+
+class Solution:
+    # @param {string} s
+    # @return {string[]}
+    def restoreIpAddresses(self, s):
+        res = []
+        cand = []
+        self.restore_ip(s, cand, res)
+        return res
+
+    def restore_ip(self, s, cand, res):
+        # If more than 4 parts, or 4 parts already but with remaining
+        # unprocessed sub-string
+        if len(cand) > 4 or len(cand) == 4 and s:
+            return
+        elif not s and len(cand) == 4:
+                res.append('.'.join(cand))
+        else:
+            k = min(3, len(s))  # Ensures s[:j + 1] won't be duplicate
+            for j in range(k):
+                b = s[:j + 1]
+                if self.is_valid_byte(b):
+                    cand.append(b)
+                    self.restore_ip(s[j + 1:], cand, res)
+                    cand.pop()
+
+    def is_valid_byte(self, b):
+        if b == '0':
+            return True
+        elif b.startswith('0'):
+            return False
+        else:
+            return int(b) < 256
+
+a = "25525511135"
+b = "010010"
+s = Solution()
+print(s.restoreIpAddresses(a))
+print(s.restoreIpAddresses(b))