add 788

fishercoder1534 · fishercoder1534 · commit addbe74b4a29 · 2018-02-25T14:10:43.000-08:00
diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|788|[Rotated Digits](https://leetcode.com/problems/rotated-digits/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_788.java) | O(n*m) | O(1) | |Easy|
 |784|[Letter Case Permutation](https://leetcode.com/problems/letter-case-permutation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_784.java) | O(n*2^n) | O(n*2^n) | |Easy|
 |783|[Minimum Distance Between BST Nodes](https://leetcode.com/problems/minimum-distance-between-bst-nodes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_783.java) | O(n) | O(h) | |Easy|
 |779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_779.java) | O(logn) | O(1) | |Medium|
diff --git a/src/main/java/com/fishercoder/solutions/_788.java b/src/main/java/com/fishercoder/solutions/_788.java
@@ -0,0 +1,62 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 788. Rotated Digits
+ *
+ * X is a good number if after rotating each digit individually by 180 degrees,
+ * we get a valid number that is different from X.
+ * A number is valid if each digit remains a digit after rotation.
+ * 0, 1, and 8 rotate to themselves;
+ * 2 and 5 rotate to each other;
+ * 6 and 9 rotate to each other,
+ * and the rest of the numbers do not rotate to any other number.
+
+ Now given a positive number N, how many numbers X from 1 to N are good?
+
+ Example:
+ Input: 10
+ Output: 4
+
+ Explanation:
+ There are four good numbers in the range [1, 10] : 2, 5, 6, 9.
+ Note that 1 and 10 are not good numbers, since they remain unchanged after rotating.
+
+ Note: N  will be in range [1, 10000].
+ */
+public class _788 {
+  public static class Solution1 {
+    public int rotatedDigits(int N) {
+      int count = 0;
+      Map<Character, String> map = new HashMap<>();
+      map.put('0', "0");
+      map.put('1', "1");
+      map.put('8', "8");
+      map.put('2', "5");
+      map.put('5', "2");
+      map.put('6', "9");
+      map.put('9', "6");
+      for (int i = 1; i <= N; i++) {
+        if (isRotatedNumber(i, map)) {
+          count++;
+        }
+      }
+      return count;
+    }
+
+    private boolean isRotatedNumber(int num, Map<Character, String> map) {
+      String originalNum = String.valueOf(num);
+      StringBuilder sb = new StringBuilder();
+      for (char c : String.valueOf(num).toCharArray()) {
+        if (!map.containsKey(c)) {
+          return false;
+        } else {
+          sb.append(map.get(c));
+        }
+      }
+      return !originalNum.equals(sb.toString());
+    }
+  }
+}
diff --git a/src/test/java/com/fishercoder/_788Test.java b/src/test/java/com/fishercoder/_788Test.java
@@ -0,0 +1,21 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._788;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _788Test {
+  private static _788.Solution1 solution1;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _788.Solution1();
+  }
+
+  @Test
+  public void test1() {
+    assertEquals(4, solution1.rotatedDigits(10));
+  }
+}
