solve problem Longest Palindrome

Author: P-ppc

README.md

@@ -108,6 +108,7 @@ All solutions will be accepted!
 |110|[Balanced Binary Tree](https://leetcode-cn.com/problems/balanced-binary-tree/description/)|[java/py/js](./algorithms/BalancedBinaryTree)|Easy|
 |70|[Climbing Stairs](https://leetcode-cn.com/problems/climbing-stairs/description/)|[java/py/js](./algorithms/ClimbingStairs)|Easy|
 |448|[Find All Numbers Disappeared In An Array](https://leetcode-cn.com/problems/find-all-numbers-disappeared-in-an-array/description/)|[java/py/js](./algorithms/FindAllNumbersDisappearedInAnArray)|Easy|
+|409|[Longest Palindrome](https://leetcode-cn.com/problems/longest-palindrome/description/)|[java/py/js](./algorithms/LongestPalindrome)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/LongestPalindrome/README.md

@@ -0,0 +1,2 @@
+# Longest Palindrome
+This problem is easy to solve

algorithms/LongestPalindrome/Solution.java

@@ -0,0 +1,21 @@
+class Solution {
+    public int longestPalindrome(String s) {
+        Map<Character, Integer> appearedMap = new HashMap<Character, Integer>();
+        int count = 0;
+        
+        for (char c : s.toCharArray()) {
+            if (appearedMap.get(c) == null) {
+                appearedMap.put(c, 1);
+            } else {
+                count += 2;
+                appearedMap.remove(c);
+            }
+        }
+        
+        if (s.length() > count) {
+            count++;
+        }
+        
+        return count;
+    }
+}

algorithms/LongestPalindrome/solution.js

@@ -0,0 +1,23 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var longestPalindrome = function(s) {
+    let appearedMap = {},
+        count = 0
+    
+    s.split('').forEach(c => {
+        if (appearedMap[c] === undefined) {
+            appearedMap[c] = 1
+        } else {
+            count += 2
+            delete appearedMap[c]
+        }
+    })
+    
+    if (s.length > count) {
+        count++
+    }
+    
+    return count
+};

algorithms/LongestPalindrome/solution.py

@@ -0,0 +1,20 @@
+class Solution(object):
+    def longestPalindrome(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        appeared_map = {}
+        count = 0
+        
+        for c in s:
+            if appeared_map.get(c) == None:
+                appeared_map[c] = 1
+            else:
+                count += 2
+                del appeared_map[c]
+        
+        if len(s) > count:
+            count += 1
+        
+        return count