add 393

Author: fishercoder1534

README.md

@@ -167,6 +167,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |398|[Random Pick Index](https://leetcode.com/problems/random-pick-index/)|[Solution](../master/src/main/java/com/fishercoder/solutions/RandomPickIndex.java) | | | Medium| Reservoir Sampling
 |397|[Integer Replacement](https://leetcode.com/problems/integer-replacement/)|[Solution](../master/src/main/java/com/fishercoder/solutions/IntegerReplacement.java)| ? | ? | Easy| BFS
 |396|[Rotate Function](https://leetcode.com/problems/rotate-function/)|[Solution](../master/src/main/java/com/fishercoder/solutions/RotateFunction.java)| O(n^2) could be optimized to O(n) | O(1) | Easy|
+|393|[UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_393.java)| O(?)|O(?) | Medium| Bit Manipulation
 |392|[Is Subsequence](https://leetcode.com/problems/is-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_392.java)| O(m*n)|O(1) | Medium| Array, String
 |390|[Elimination Game](https://leetcode.com/problems/elimination-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/EliminationGame.java)| O(logn)|O(1) | Medium|
 |389|[Find the Difference](https://leetcode.com/problems/find-the-difference/)|[Solution](../master/src/main/java/com/fishercoder/solutions/FindTheDifference.java)| O(n)|O(1) | Easy|

src/main/java/com/fishercoder/solutions/_393.java

@@ -38,22 +38,21 @@
  */
 public class _393 {
 
+    /**credit: https://discuss.leetcode.com/topic/58338/bit-manipulation-java-6ms/4*/
     public boolean validUtf8(int[] data) {
-        //TODO: not finished yet
-        if (data == null || data.length == 0 || data.length > 4) return false;
-        int len = data.length;
-        String[] last8Bits = new String[len];
-        for (int i = 0; i < len; i++) {
-            String bin = Integer.toBinaryString(data[i]);
-            last8Bits[i] = bin.length() >= 8 ? bin.substring(0, 8) : String.format("%08d", Integer.parseInt(bin));//pad left with zeroes to make sure each number is 8 bits long to make coding easier in the later part
+        int count = 0;
+        for(int d:data){
+            if(count == 0){
+                if((d >> 5) == 0b110) count = 1;
+                else if((d >> 4) == 0b1110) count = 2;
+                else if((d >> 3) == 0b11110) count = 3;
+                else if((d >> 7) ==  1) return false;
+            } else {
+                if((d>>6) != 0b10) return false;
+                else count--;
+            }
         }
-        if (len == 1) {
-            if (Integer.valueOf(last8Bits[0].substring(0,1)) != 0) return false;
-            return true;
-        } else {
-
-        }
-        return false;
+        return count == 0;
     }
 
 }