solves #246: Strobogrammatic Number in java

Author: anishLearnsToCode

README.md

@@ -215,8 +215,8 @@
 | 243  | 🔒 [Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance)                                                                                      |                                                                                    [![Java](assets/java.png)](src/ShortestWordDistance.java)                                                                                     |                                                                                                                                   |
 | 244  | 🔒 [Shortest Word Distance II](https://leetcode.com/problems/shortest-word-distance-ii)                                                                                |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 245  | 🔒 [Shortest Word Distance III](https://leetcode.com/problems/shortest-word-distance-iii)                                                                              |                                                                                                                                                                                                                                  |                                                                                                                                   |
-| 246  | 🔒 [Strobogramatic Number](https://leetcode.com/problems/strobogrammatic-number)                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
-| 247  | 🔒 [Strobogramatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii)                                                                                 |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 246  | 🔒 [Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number)                                                                                      |                                                                                    [![Java](assets/java.png)](src/StrobogrammaticNumber.java)                                                                                    |                                                                                                                                   |
+| 247  | 🔒 [Strobogrammatic Number II](https://leetcode.com/problems/strobogrammatic-number-ii)                                                                                |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 249  | 🔒 [Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings)                                                                                        |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 250  | 🔒 [Count Univalue Subtrees](https://leetcode.com/problems/count-univalue-subtrees)                                                                                    |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 251  | 🔒 [Flatten 2D Vector](https://leetcode.com/problems/flatten-2d-vector)                                                                                                |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/StrobogrammaticNumber.java

@@ -0,0 +1,30 @@
+// https://leetcode.com/problems/strobogrammatic-number
+// T: O(N)
+// S: O(1)
+
+import java.util.HashMap;
+import java.util.Map;
+
+// Strobogrammatic digits: 0, 1, 8
+// Strobogrammatic interchangeable digits: 6 --> 9, 9 --> 6
+public class StrobogrammaticNumber {
+    private static final Map<Character, Character> STROBOGRAMMATIC_MIRROR = new HashMap<>() {{
+        put('0', '0');
+        put('1', '1');
+        put('6', '9');
+        put('8', '8');
+        put('9', '6');
+    }};
+
+    public boolean isStrobogrammatic(String number) {
+        for (int i = 0 ; i < number.length() ; i++) {
+            final char digit = number.charAt(i);
+            if (!STROBOGRAMMATIC_MIRROR.containsKey(digit)
+                    || STROBOGRAMMATIC_MIRROR.get(digit) != number.charAt(number.length() - 1 - i)
+            ) {
+                return false;
+            }
+        }
+        return true;
+    }
+}