New Problem Solution "Longest Palindrome"

README.md

@@ -12,6 +12,7 @@ LeetCode
 |414|[Third Maximum Number](https://leetcode.com/problems/third-maximum-number/) | [C++](./algorithms/cpp/thirdMaximumNumber/ThirdMaximumNumber.cpp)|Easy|
 |413|[Arithmetic Slices](https://leetcode.com/problems/arithmetic-slices/) | [C++](./algorithms/cpp/arithmeticSlices/ArithmeticSlices.cpp)|Medium|
 |412|[Fizz Buzz](https://leetcode.com/problems/fizz-buzz/) | [C++](./algorithms/cpp/fizzBuzz/FizzBuzz.cpp)|Easy|
+|409|[Longest Palindrome](https://leetcode.com/problems/longest-palindrome/) | [C++](./algorithms/cpp/longestPalindrome/LongestPalindrome.cpp)|Easy|
 |406|[Queue Reconstruction by Height](https://leetcode.com/problems/queue-reconstruction-by-height/) | [C++](./algorithms/cpp/queueReconstructionByHeight/QueueReconstructionByHeight.cpp)|Medium|
 |405|[Convert a Number to Hexadecimal](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) | [C++](./algorithms/cpp/convertANumberToHexadecimal/ConvertANumberToHexadecimal.cpp)|Easy|
 |404|[Sum of Left Leaves](https://leetcode.com/problems/sum-of-left-leaves/) | [C++](./algorithms/cpp/sumOfLeftLeaves/SumOfLeftLeaves.cpp)|Easy|

algorithms/cpp/longestPalindrome/LongestPalindrome.cpp

@@ -0,0 +1,50 @@
+// Source : https://leetcode.com/problems/longest-palindrome/
+// Author : Hao Chen
+// Date   : 2016-11-13
+
+/*************************************************************************************** 
+ *
+ * Given a string which consists of lowercase or uppercase letters, find the length of 
+ * the longest palindromes that can be built with those letters.
+ * 
+ * This is case sensitive, for example "Aa" is not considered a palindrome here.
+ * 
+ * Note:
+ * Assume the length of given string will not exceed 1,010.
+ * 
+ * Example: 
+ * 
+ * Input:
+ * "abccccdd"
+ * 
+ * Output:
+ * 7
+ * 
+ * Explanation:
+ * One longest palindrome that can be built is "dccaccd", whose length is 7.
+ ***************************************************************************************/
+
+class Solution {
+public:
+    int longestPalindrome(string s) {
+        
+        int hashtable[128];
+        memset(hashtable, 0, sizeof(hashtable));
+        
+        for(char ch : s) {
+            hashtable[ch]++;
+        }
+        int result = 0;
+        bool hasOdd = false;
+        for (int n : hashtable) {
+            if ( n%2 == 0 ) {
+                result += n;
+            } else {
+                result += n -1;
+                hasOdd = true;
+            }
+        }
+        
+        return hasOdd ? result + 1 : result;
+    }
+};