feat: add solution of Longest Common Prefix(014) with kotlin.

Author: relish-wang

README.md

@@ -28,7 +28,7 @@
 | [007][007-question] | [Reverse Integer][007-tips]                                  | [✅][007-java] | [✅][007-js] | [✅][007-kotlin] |
 | [009][009-question] | [Palindrome Number][009-tips]                                | [✅][009-java] |              | [✅][009-kotlin] |
 | [013][013-question] | [Roman to Integer][013-tips]                                 | [✅][013-java] |              | [✅][013-kotlin] |
-| [014][014-question] | [Longest Common Prefix][014-tips]                            | [✅][014-java] |              |                  |
+| [014][014-question] | [Longest Common Prefix][014-tips]                            | [✅][014-java] |              | [✅][014-kotlin] |
 | [020][020-question] | [Valid Parentheses][020-tips]                                | [✅][020-java] |              |                  |
 | [021][021-question] | [Merge Two Sorted Lists][021-tips]                           | [✅][021-java] |              |                  |
 | [026][026-question] | [Remove Duplicates from Sorted Array][026-tips]              | [✅][026-java] |              |                  |
@@ -452,4 +452,5 @@
 [007-kotlin]: ./src/_007/kotlin/Solution.kt
 [009-kotlin]: ./src/_009/kotlin/Solution.kt
 [013-kotlin]: ./src/_013/kotlin/Solution.kt
+[014-kotlin]: ./src/_014/kotlin/Solution.kt
 [771-kotlin]: ./src/_771/kotlin/Solution.kt

lib/kotlin-reflect.jar

@@ -0,0 +1,32 @@
+package _014.kotlin
+
+/**
+ * @author relish
+ * @since 2018/04/09
+ */
+class Solution {
+    fun longestCommonPrefix(strs: Array<String>): String {
+        if (strs.isEmpty()) return ""
+        var ret = ""
+        for (i in 0 until strs[0].length) {
+            val ch = strs[0][i]
+            for (str in strs) {
+                if (str.length <= i) return ret
+                if (ch != str[i]) return ret
+            }
+            ret += ch
+        }
+        return ret
+    }
+}
+
+fun main(args: Array<String>) {
+    val strs = Array(5, { "" })
+    strs[0] = "abcdefg"
+    strs[1] = "abcdfefg"
+    strs[2] = "abcdgefg"
+    strs[3] = "abcddefg"
+    strs[4] = "abce"
+
+    println(Solution().longestCommonPrefix(strs))
+}

lib/kotlin-stdlib-sources.jar

@@ -11,6 +11,7 @@ Write a function to find the longest common prefix string amongst an array of st
 
 题意是让你从字符串数组中找出公共前缀，我的想法是找出最短的那个字符串的长度 `minLen`，然后在 `0...minLen` 的范围比较所有字符串，如果比较到有不同的字符，那么直接返回当前索引长度的字符串即可，否则最后返回最短的字符串即可。
 
+java:
 ```java
 class Solution {
     public String longestCommonPrefix(String[] strs) {
@@ -27,6 +28,29 @@ class Solution {
 }
 ```
 
+与java的解法思路大致相同, 不过少了`找出最短的那个字符串的长度 minLen`这个环节。
+我直接假定字符串数组里的第一个字符串的长度是最短的,->`for (i in 0 until strs[0].length) {`  
+后面在遍历时遇到长度小于等于index的字符串时，直接返回结果.->`if (str.length <= i) return ret`  
+(也有可能在此之前就返回了结果)。->`if (ch != str[i]) return ret`  
+kotlin:
+```kotlin
+class Solution {
+    fun longestCommonPrefix(strs: Array<String>): String {
+        if (strs.isEmpty()) return ""
+        var ret = ""
+        for (i in 0 until strs[0].length) {
+            val ch = strs[0][i]
+            for (str in strs) {
+                if (str.length <= i) return ret
+                if (ch != str[i]) return ret
+            }
+            ret += ch
+        }
+        return ret
+    }
+}
+```
+
 
 ## 结语