LongestPalindrome409

Author: fluency03

README.md

@@ -53,11 +53,11 @@
 | [Graph](https://github.com/fluency03/leetcode-java/blob/master/src/graph) |
 
 
-# Total: 494
+# Total: 495
 
 |   Easy  |  Medium | Hard | - |
 |:-------:|:-------:|:----:|:-:|
-|   131   |   272   |  81  | 10 |
+|   132   |   272   |  81  | 10 |
 
 
 | Question | Solution | Difficulty |
@@ -362,6 +362,7 @@
 | [405. Convert a Number to Hexadecimal](https://leetcode.com/problems/convert-a-number-to-hexadecimal/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ConvertANumberToHexadecimal405.java) | Easy |
 | [406. Queue Reconstruction by Height](https://leetcode.com/problems/queue-reconstruction-by-height/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/QueueReconstructionByHeight406.java) | Medium |
 | [407. Trapping Rain Water II](https://leetcode.com/problems/trapping-rain-water-ii/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/TrappingRainWaterII407.java) | Medium |
+| [409. Longest Palindrome](https://leetcode.com/problems/longest-palindrome/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/LongestPalindrome409.java) | Easy |
 | [410. Split Array Largest Sum](https://leetcode.com/problems/split-array-largest-sum/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/SplitArrayLargestSum410.java) | Hard |
 | [414. Third Maximum Number](https://leetcode.com/problems/third-maximum-number/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/ThirdMaximumNumber414.java) | Easy |
 | [415. Add Strings](https://leetcode.com/problems/add-strings/) | [Solution](https://github.com/fluency03/leetcode-java/blob/master/src/AddStrings415.java) | Easy |

src/LongestIncreasingSubsequence300.java

@@ -34,6 +34,7 @@ public int lengthOfLIS(int[] nums) {
 
     /**
      * https://leetcode.com/problems/longest-increasing-subsequence/solution/
+     * https://www.geeksforgeeks.org/longest-monotonically-increasing-subsequence-size-n-log-n/
      */
     public int lengthOfLIS2(int[] nums) {
         int[] dp = new int[nums.length];

src/LongestPalindrome409.java

@@ -0,0 +1,75 @@
+/**
+ * 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.
+ */
+
+public class LongestPalindrome409 {
+    public int longestPalindrome(String s) {
+        Map<Character, Integer> map = new HashMap<>();
+        for (char ch: s.toCharArray()) {
+            map.put(ch, map.getOrDefault(ch, 0) + 1);
+        }
+        
+        int res = 0;
+        boolean hasOdd = false;
+        for (int i: map.values()) {
+            if (i % 2 == 0) {
+                res += i;
+            } else {
+                res += i - 1;
+                hasOdd = true;
+            }
+        }
+        return res + (hasOdd ? 1 : 0);
+    }
+
+
+    /**
+     * https://leetcode.com/problems/longest-palindrome/discuss/89604/Simple-HashSet-solution-Java
+     */
+    public int longestPalindrome2(String s) {
+        if(s==null || s.length()==0) return 0;
+        HashSet<Character> hs = new HashSet<Character>();
+        int count = 0;
+        for(int i=0; i<s.length(); i++){
+            if(hs.contains(s.charAt(i))){
+                hs.remove(s.charAt(i));
+                count++;
+            }else{
+                hs.add(s.charAt(i));
+            }
+        }
+        if(!hs.isEmpty()) return count*2+1;
+        return count*2;
+    }
+
+
+    /**
+     * https://leetcode.com/problems/longest-palindrome/discuss/89610/Simple-Java-Solution-in-One-Pass
+     */
+    public int longestPalindrome3(String s) {
+        boolean[] map = new boolean[128];
+        int len = 0;
+        for (char c : s.toCharArray()) {
+            map[c] = !map[c];         // flip on each occurrence, false when seen n*2 times
+            if (!map[c]) len+=2;
+        }
+        if (len < s.length()) len++; // if more than len, atleast one single is present
+        return len;
+    }
+
+}