add palindrome number

Steve Sun · Steve Sun · commit 30043f4c962c · 2016-10-12T21:23:21.000-07:00
diff --git a/EASY/src/easy/PalindromeNumber.java b/EASY/src/easy/PalindromeNumber.java
@@ -0,0 +1,20 @@
+package easy;
+
+public class PalindromeNumber {
+    
+    /**Purely my original solution: just reverse the entire number and compare with itself, return if they two are equal or not.*/
+    public boolean isPalindrome(int x) {
+        if(x == 0) return true;
+        if(x < 0) return false;
+        int rev = 0, tmp = x;
+        while(tmp != 0){
+            rev *= 10;
+            rev += tmp%10;
+            tmp /= 10;
+        }
+        return rev == x;
+    }
+    
+    /**Then I turned to Discuss and found a more efficient way: reversing only half and then compare if they're equal.*/
+
+}
diff --git a/README.md b/README.md
@@ -47,6 +47,7 @@
 |17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Solution](../../blob/master/MEDIUM/src/medium/LetterCombinationsofaPhoneNumber.java)|O(n*4^n)|O(n)|Medium|Backtracking
 |15|[3Sum](https://leetcode.com/problems/3sum/)|[Solution](../../blob/master/MEDIUM/src/medium/_3Sum.java)|O(nlogn)|O(1)|Medium|Two Pointers
 |10|[Regular Expression Matching](https://leetcode.com/problems/regular-expression-matching/)|[Solution](../../blob/master/HARD/src/hard/RegularExpressionMatching.java)|O(m*n)|O(m*n)|Hard|DP
+|9|[Palindrome Number](https://leetcode.com/problems/palindrome-number/)|[Solution](../../blob/master/EASY/src/easy/PalindromeNumber.java)| O(logn)/(n) | O(1) | Easy
 |8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/)|[Solution](../../blob/master/EASY/src/easy/StringToInteger.java)| O(n) | O(1) | Easy
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/)|[Solution](../../blob/master/EASY/src/easy/ReverseInteger.java) | O(1) | O(1) | Easy | 
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)|[Solution](../../blob/master/MEDIUM/src/medium/AddTwoNumbers.java) | O(n) | O(1) | Medium | LinkedList
