solves restores ip addresses in java

Author: anishLearnsToCode

README.md

@@ -83,7 +83,7 @@
 |  90  | [Subsets II](https://leetcode.com/problems/subsets-ii)                                                                                                    |                                                                    [![Java](assets/java.png)](src/SubsetsII.java)                                                                    |                                                                                                                                   |
 |  91  | [Decode Ways](https://leetcode.com/problems/decode-ways)                                                                                                  |                                                                   [![Java](assets/java.png)](src/DecodeWays.java)                                                                    |                                                                                                                                   |
 |  92  | [Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii)                                                                            |                                                               [![Java](assets/java.png)](src/ReverseLinkedListII.java)                                                               |                                                                                                                                   |
-|  93  | [Restore IP Addresses](https://leetcode.com/problems/restore-ip-addresses)                                                                                |                                                                                                                                                                                      |                                                                                                                                   |
+|  93  | [Restore IP Addresses](https://leetcode.com/problems/restore-ip-addresses)                                                                                |                                                               [![Java](assets/java.png)](src/RestoreIPAddresses.java)                                                                |                                                                                                                                   |
 |  94  | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)                                                             |                       [![Java](assets/java.png)](src/BinaryTreeInorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_inorder_traversal.py)                        |                                                                                                                                   |
 |  95  | [Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii)                                                              |                                                                                                                                                                                      |                                                                                                                                   |
 |  96  | [Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees)                                                                    |                                                                                                                                                                                      |                                                                                                                                   |

src/RestoreIPAddresses.java

@@ -0,0 +1,57 @@
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+public class RestoreIPAddresses {
+    public List<String> restoreIpAddresses(final String s) {
+        final List<String> result = new ArrayList<>();
+        restoreIpAddresses(s, result, new LinkedList<>(), 0);
+        return result;
+    }
+
+    private void restoreIpAddresses(final String s, final List<String> result, LinkedList<Integer> numbers, int index) {
+        if (numbers.size() == 4 && index == s.length()) {
+            result.add(ipAddressFrom(numbers));
+            return;
+        }
+        if (numbers.size() >= 4 || index == s.length()) {
+            return;
+        }
+        for (int i = index + 1 ; i <= s.length() ; i++) {
+            if (isValidIpAddressInteger(s, index, i)) {
+                numbers.add(toNumber(s, index, i));
+                restoreIpAddresses(s, result, numbers, i);
+                numbers.removeLast();
+            } else {
+                break;
+            }
+        }
+    }
+
+    private String ipAddressFrom(LinkedList<Integer> numbers) {
+        StringBuilder result = new StringBuilder();
+        for (int number : numbers) {
+            result.append(number).append('.');
+        }
+        result.deleteCharAt(result.length() - 1);
+        return result.toString();
+    }
+
+    private boolean isValidIpAddressInteger(String s, int start, int end) {
+        if (hasLeadingZeros(s, start, end)) return false;
+        return toNumber(s, start, end) < 256;
+    }
+
+    private boolean hasLeadingZeros(String s, int start, int end) {
+        return end - start > 1 && s.charAt(start) == '0';
+    }
+
+    private int toNumber(String s, int start, int end) {
+        int val = 0;
+        for (int index = start ; index < end ; index++) {
+            val *= 10;
+            val += s.charAt(index) - '0';
+        }
+        return val;
+    }
+}