[LEET-93] add 93

Author: fishercoder1534

leetcode-algorithms/README.md

@@ -259,6 +259,7 @@
 |96|[Unique Binary Search Trees](https://leetcode.com/problems/unique-binary-search-trees/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/UniqueBinarySearchTrees.java) | O(n^2) | O(n) | Medium | Recursion, DP
 |95|[Unique Binary Search Trees II](https://leetcode.com/problems/unique-binary-search-trees-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/UniqueBinarySearchTreesII.java) | O(?) | O(?) | Medium | Recursion
 |94|[Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/BinaryTreeInorderTraversal.java)| O(n)|O(h) | Medium| Binary Tree
+|93|[Restore IP Addresses](https://leetcode.com/problems/restore-ip-addresses/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/RestoreIPAddresses.java)| O(1)|O(1) | Medium | Backtracking
 |92|[Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ReverseLinkedListII.java)| O(n)|O(1) | Medium
 |91|[Decode Ways](https://leetcode.com/problems/decode-ways/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/DecodeWays.java)| O(n)|O(n) | Medium| DP
 |89|[Gray Code](https://leetcode.com/problems/gray-code/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/GrayCode.java)|O(n) |O(1)|Medium|Bit Manipulation

leetcode-algorithms/src/main/java/com/stevesun/solutions/RestoreIPAddresses.java

@@ -0,0 +1,52 @@
+package com.stevesun.solutions;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 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)
+ */
+public class RestoreIPAddresses {
+
+    public List<String> restoreIpAddresses(String s) {
+        List<String> allValidIpAddresses = new ArrayList<>();
+        if (s == null || s.length() > 12 || s.length() < 4) return allValidIpAddresses;
+        backtracking(s, new ArrayList<>(), allValidIpAddresses, 0);
+        return allValidIpAddresses;
+    }
+
+    private void backtracking(String s, ArrayList<String> bytes, List<String> result, int pos) {
+        if (bytes.size() == 4) {
+            if (pos != s.length()) return;
+            StringBuilder stringBuilder = new StringBuilder();
+            for (int i = 0; i < 4; i++) {
+                stringBuilder.append(bytes.get(i));
+                stringBuilder.append(".");
+            }
+            stringBuilder.setLength(stringBuilder.length()-1);
+            result.add(stringBuilder.toString());
+            return;
+        }
+
+        for (int i = pos; i < pos+4 && i < s.length(); i++) {
+            String oneByte = s.substring(pos, i+1);
+            if (!isValid(oneByte)) continue;
+            bytes.add(oneByte);
+            backtracking(s, bytes, result, i+1);
+            bytes.remove(bytes.size()-1);
+        }
+    }
+
+    private boolean isValid(String oneByte) {
+        if (oneByte.charAt(0) == '0') return oneByte.equals("0");
+        int num = Integer.valueOf(oneByte);
+        return (num >= 0 && num < 256);
+    }
+
+
+}

leetcode-algorithms/src/test/java/com/stevesun/RestoreIPAddressesTest.java

@@ -0,0 +1,38 @@
+package com.stevesun;
+
+import com.stevesun.solutions.RestoreIPAddresses;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static junit.framework.Assert.assertEquals;
+
+public class RestoreIPAddressesTest {
+    private static RestoreIPAddresses test;
+    private static List<String> expected;
+    private static List<String> actual;
+    private static String s;
+
+    @BeforeClass
+    public static void setup(){
+        test = new RestoreIPAddresses();
+    }
+
+    @Before
+    public void setupForEachTest(){
+        expected = new ArrayList<>();
+        actual = new ArrayList<>();
+    }
+
+    @Test
+    public void test1(){
+        s = "25525511135";
+        expected.add("255.255.11.135");
+        expected.add("255.255.111.35");
+        actual = test.restoreIpAddresses(s);
+        assertEquals(expected, actual);
+    }
+}