New Problem Solution "UTF-8 Validation"

haoel · haoel · commit cfe88095df07 · 2016-09-08T01:44:30.000+08:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|393|[UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/) | [C++](./algorithms/cpp/UTF8Validation/UTF8Validation.cpp)|Medium|
 |392|[Is Subsequence](https://leetcode.com/problems/is-subsequence/) | [C++](./algorithms/cpp/isSubsequence/IsSubsequence.cpp)|Medium|
 |391|[Perfect Rectangle](https://leetcode.com/problems/perfect-rectangle/) | [C++](./algorithms/cpp/perfectRectangle/PerfectRectangle.cpp)|Hard|
 |390|[Elimination Game](https://leetcode.com/contest/2/problems/elimination-game/) | [C++](./algorithms/cpp/eliminationGame/EliminationGame.cpp)|Medium|
diff --git a/algorithms/cpp/UTF8Validation/UTF8Validation.cpp b/algorithms/cpp/UTF8Validation/UTF8Validation.cpp
@@ -0,0 +1,86 @@
+// Source : https://leetcode.com/problems/utf-8-validation/
+// Author : Hao Chen
+// Date   : 2016-09-08
+
+/*************************************************************************************** 
+ *
+ * A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:
+ * 
+ * For 1-byte character, the first bit is a 0, followed by its unicode code.
+ * For n-bytes character, the first n-bits are all one's, the n+1 bit is 0, followed by 
+ * n-1 bytes with most significant 2 bits being 10.
+ * 
+ * This is how the UTF-8 encoding would work:
+ * 
+ *    Char. number range  |        UTF-8 octet sequence
+ *    --------------------+---------------------------------------------
+ *    0000 0000-0000 007F | 0xxxxxxx
+ *    0000 0080-0000 07FF | 110xxxxx 10xxxxxx
+ *    0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx
+ *    0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
+ * 
+ * Given an array of integers representing the data, return whether it is a valid utf-8 
+ * encoding.
+ * 
+ * Note:
+ * The input is an array of integers. Only the least significant 8 bits of each integer 
+ * is used to store the data. This means each integer represents only 1 byte of data.
+ * 
+ * Example 1:
+ * 
+ * data = [197, 130, 1], which represents the octet sequence: 11000101 10000010 
+ * 00000001.
+ * 
+ * Return true.
+ * It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.
+ * 
+ * Example 2:
+ * 
+ * data = [235, 140, 4], which represented the octet sequence: 11101011 10001100 
+ * 00000100.
+ * 
+ * Return false.
+ * The first 3 bits are all one's and the 4th bit is 0 means it is a 3-bytes character.
+ * The next byte is a continuation byte which starts with 10 and that's correct.
+ * But the second continuation byte does not start with 10, so it is invalid.
+ ***************************************************************************************/
+
+
+class Solution {
+public:
+    bool validUtf8(vector<int>& data) {
+        int i = 0;
+        while ( i < data.size() ) {
+            if ( (data[i] & 0x80) == 0 ){
+                i++;
+                continue;
+            }
+            
+            int len = 0;
+            if ( (data[i] & 0xE0) == 0xC0 ) { // checking 110xxxxx
+                len = 2;
+            }else if ( (data[i] & 0xF0) == 0xE0) { // checking 1110xxxx
+                len = 3;
+            }else if ( (data[i] & 0xF8) == 0xF0) { // checking 11110xxx
+                len = 4;
+            }else {
+                return false;
+            }
+            
+            
+            for (int j=i+1; j < i+len; j++) { //checking 10xxxxxx
+                if ( (data[j] & 0xC0) != 0x80 ) {
+                    return false;
+                }
+            }
+            
+            i += len ;
+            
+            if (i > data.size()) {
+                return false;
+            }
+            
+        }
+        return true;
+    }
+};
