restore ip address

Author: zgpeace

code/LeetCode/src/backtracking/RestoreIPAddress.java

@@ -0,0 +1,50 @@
+package backtracking;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+// https://leetcode.com/problems/restore-ip-addresses/
+public class RestoreIPAddress {
+
+  public static void main(String[] args) {
+    RestoreIPAddress obj = new RestoreIPAddress();
+    String s = "25525511135";
+    List<String> resultList = obj.restoreIpAddresses(s);
+    System.out.println(Arrays.toString(resultList.toArray()));
+  }
+
+  public List<String> restoreIpAddresses(String s) {
+    List<String> resultList = new ArrayList<String>();
+    if (s == null || s.length() < 4) {
+      return resultList;
+    }
+
+    // DFS
+    dfs(resultList, s, 0, "", 0);
+
+    return resultList;
+  }
+
+  private void dfs(List<String> resultList, String s, int start, String stored, int count) {
+    //exit
+    if (start == s.length() && count == 4) {
+        resultList.add(stored);
+    }
+
+    if (start == s.length() || count == 4) {
+      return;
+    }
+
+    for (int i = 1; i < 4; i++) {
+      if (start + i > s.length()) {
+        break;
+      }
+      String part = s.substring(start, start + i);
+      if ((part.startsWith("0") && part.length() > 1) || (i == 3 && Integer.valueOf(part) > 255)) {
+        continue;
+      }
+      dfs(resultList, s, start + i, stored + part + (count == 3 ? "" : "."), count + 1);
+    }
+  }
+}