feat: add the solution of Sqrt(x)(069) with kotlin.

Author: relish-wang

README.md

@@ -43,7 +43,7 @@
 | [058][058-question] | [Length of Last Word][058-tips]                              | [✅][058-java] |              | [✅][058-kotlin] |
 | [066][066-question] | [Plus One][066-tips]                                         | [✅][066-java] |              | [✅][066-kotlin] |
 | [067][067-question] | [Add Binary][067-tips]                                       | [✅][067-java] |              | [✅][067-kotlin] |
-| [069][069-question] | [Sqrt(x)][069-tips]                                          | [✅][069-java] |              |                  |
+| [069][069-question] | [Sqrt(x)][069-tips]                                          | [✅][069-java] |              | [✅][069-kotlin] |
 | [070][070-question] | [Climbing Stairs][070-tips]                                  | [✅][070-java] |              |                  |
 | [083][083-question] | [Remove Duplicates from Sorted List][083-tips]               | [✅][083-java] |              |                  |
 | [088][088-question] | [Merge Sorted Array][088-tips]                               | [✅][088-java] |              |                  |
@@ -487,4 +487,5 @@
 [058-kotlin]: ./src/_058/kotlin/Solution.kt
 [066-kotlin]: ./src/_066/kotlin/Solution.kt
 [067-kotlin]: ./src/_067/kotlin/Solution.kt
+[069-kotlin]: ./src/_069/kotlin/Solution.kt
 [771-kotlin]: ./src/_771/kotlin/Solution.kt

src/_069/kotlin/Solution.kt

@@ -0,0 +1,20 @@
+package _069.kotlin
+
+/**
+ * @author relish
+ * @since 2018/04/21
+ */
+class Solution {
+    fun mySqrt(x: Int): Int {
+        var k = x.toLong()
+        while (k * k > x)
+            k = (k + x / k) / 2
+        return k.toInt()
+    }
+}
+
+fun main(args: Array<String>) {
+    println(Solution().mySqrt(2147395599))
+    println(Solution().mySqrt(8))
+    println(Solution().mySqrt(120))
+}

tips/069/README.md

@@ -30,6 +30,7 @@ Explanation: The square root of 8 is 2.82842..., and since we want to return an
 
 题意是求平方根，参考 [牛顿迭代法求平方根](https://wenku.baidu.com/view/6b74c622bcd126fff7050bfe.html)，然后再参考维基百科的 [Integer square root](https://en.wikipedia.org/wiki/Integer_square_root#Using_only_integer_division) 即可。
 
+java:
 ```java
 class Solution {
     public int mySqrt(int x) {
@@ -42,6 +43,18 @@ class Solution {
 }
 ```
 
+kotlin(192ms/78.57%):
+```kotlin
+class Solution {
+    fun mySqrt(x: Int): Int {
+        var k = x.toLong()
+        while (k * k > x)
+            k = (k + x / k) / 2
+        return k.toInt()
+    }
+}
+```
+
 
 ## 结语