feat: add the solution of Valid Palindrome(125) with kotlin.

Author: relish-wang

README.md

@@ -85,6 +85,7 @@
 | [119][119-question] | [Pascal's Triangle II][119-tips]                             | [Easy][E]   | [✅][119-java] |              | [✅][119-kotlin] |
 | [121][121-question] | [Best Time to Buy and Sell Stock][121-tips]                  | [Easy][E]   | [✅][121-java] |              | [✅][121-kotlin] |
 | [122][122-question] | [Best Time to Buy and Sell Stock II][122-tips]               | [Easy][E]   | [✅][122-java] |              | [✅][122-kotlin] |
+| [125][125-question] | [Valid Palindrome][125-tips]                                 | [Easy][E]   |                |              | [✅][125-kotlin] |
 | [226][226-question] | [Invert Binary Tree][226-tips]                               | [Easy][E]   | [✅][226-java] | [✅][226-js] | [✅][226-kotlin] |
 | [504][504-question] | [Base 7][504-tips]                                           | [Easy][E]   |                |              | [✅][504-kotlin] |
 | [543][543-question] | [Diameter of Binary Tree][543-tips]                          | [Easy][E]   | [✅][543-java] |              | [✅][543-kotlin] |
@@ -204,6 +205,7 @@
 [119-question]: https://leetcode.com/problems/pascals-triangle-ii/
 [121-question]: https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
 [122-question]: https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/
+[125-question]: https://leetcode.com/problems/valid-palindrome/
 [226-question]: https://leetcode.com/problems/invert-binary-tree/
 [504-question]: https://leetcode.com/problems/base-7/description/
 [543-question]: https://leetcode.com/problems/diameter-of-binary-tree/
@@ -304,6 +306,7 @@
 [119-tips]: ./tips/119/README.md
 [121-tips]: ./tips/121/README.md
 [122-tips]: ./tips/122/README.md
+[125-tips]: ./tips/125/README.md
 [226-tips]: ./tips/226/README.md
 [504-tips]: ./tips/504/README.md
 [543-tips]: ./tips/543/README.md
@@ -525,6 +528,7 @@
 [119-kotlin]: ./src/_119/kotlin/Solution.kt
 [121-kotlin]: ./src/_121/kotlin/Solution.kt
 [122-kotlin]: ./src/_122/kotlin/Solution.kt
+[125-kotlin]: ./src/_125/kotlin/Solution.kt
 [226-kotlin]: ./src/_226/kotlin/Solution.kt
 [504-kotlin]: ./src/_504/kotlin/Solution.kt
 [543-kotlin]: ./src/_543/kotlin/Solution.kt

src/_125/kotlin/Solution.kt

@@ -0,0 +1,37 @@
+package _125.kotlin
+
+/**
+ * @author relish
+ * @since 2018/11/09
+ */
+class Solution {
+    fun isPalindrome(s: String): Boolean {
+        if (s == " ") return true
+        val len = s.length
+        var i = 0
+        var j = len - 1
+        while (i <= j) {
+            try {
+                while (!(s[i] in 'a'..'z' || s[i] in 'A'..'Z' || s[i] in '0'..'9')) i++
+                while (!(s[j] in 'a'..'z' || s[j] in 'A'..'Z' || s[j] in '0'..'9')) j--
+            } catch (e: Exception) {
+                return true
+            }
+            try {
+                if (!s[i++].equals(s[j--], true)) return false
+            } catch (e: Exception) {
+                return false
+            }
+        }
+        return true
+    }
+}
+
+fun main(args: Array<String>) {
+    println(Solution().isPalindrome("A man, a plan, a canal: Panama"))
+    println(Solution().isPalindrome("race a car"))
+    println(Solution().isPalindrome(" "))
+    println(Solution().isPalindrome("."))
+    println(Solution().isPalindrome("0P"))
+    println(Solution().isPalindrome("ab2a"))
+}

tips/125/README.md

@@ -0,0 +1,64 @@
+[125. Valid Palindrome][title]
+
+## Description
+Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
+
+
+**Example 1:**
+
+```
+Input: "A man, a plan, a canal: Panama"
+Output: true
+```
+**Example 2:**
+
+```
+Input: "race a car"
+Output: false
+```
+
+**Note:**
+For the purpose of this problem, we define empty string as valid palindrome.
+
+**Tags:** 
+`Two Pointers`、 `String`
+
+
+
+## 思路 1
+1 空串为true
+2 从两边往中间靠拢, 遇到不是字母也不是数字的就跳过
+3 左边游标索引大于右边游标索引则结束遍历
+4 遍历过程中一旦发生不相等, 则不是回文
+kotlin(228ms/94.44%):
+```kotlin
+class Solution {
+    fun isPalindrome(s: String): Boolean {
+        if (s == " ") return true
+        val len = s.length
+        var i = 0
+        var j = len - 1
+        while (i <= j) {
+            try {
+                while (!(s[i] in 'a'..'z' || s[i] in 'A'..'Z' || s[i] in '0'..'9')) i++
+                while (!(s[j] in 'a'..'z' || s[j] in 'A'..'Z' || s[j] in '0'..'9')) j--
+            } catch (e: Exception) {
+                return true
+            }
+            try {
+                if (!s[i++].equals(s[j--], true)) return false
+            } catch (e: Exception) {
+                return false
+            }
+        }
+        return true
+    }
+}
+```
+
+## 结语
+   
+如果你同我们一样热爱数据结构、算法、LeetCode，可以关注我们 GitHub 上的 LeetCode 题解：[LeetCode-Solution][ls]
+
+[title]: https://leetcode.com/problems/valid-palindrome/
+[ls]: https://github.com/RichCodersAndMe/LeetCode-Solution