add 028

Author: andavid

README.md

@@ -37,6 +37,7 @@
 | 242  | [Valid Anagram][242]                        |
 | 125  | [Valid Palindrome][125]                     |
 | 8    | [String to Integer (atoi)][008]             |
+| 28   | [Implement strStr()][028]                   |
 
 
 **其他**
@@ -69,3 +70,4 @@
 [242]: https://github.com/andavid/leetcode-java/blob/master/note/242/README.md
 [125]: https://github.com/andavid/leetcode-java/blob/master/note/125/README.md
 [008]: https://github.com/andavid/leetcode-java/blob/master/note/008/README.md
+[028]: https://github.com/andavid/leetcode-java/blob/master/note/028/README.md

note/028/README.md

@@ -0,0 +1,41 @@
+# [Implement strStr()][title]
+
+## Description
+
+Implement strStr().
+
+Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
+
+**Example 1:**
+
+```
+Input: haystack = "hello", needle = "ll"
+Output: 2
+```
+
+**Example 2:**
+
+```
+Input: haystack = "aaaaa", needle = "bba"
+Output: -1
+```
+
+## 思路
+
+太简单了吧，indexOf 搞定。
+
+## [完整代码][src]
+
+```java
+class Solution {
+  public int strStr(String haystack, String needle) {
+    if (null == haystack || null == needle) {
+      return -1;
+    }
+    return haystack.indexOf(needle);
+  }
+}
+```
+
+[title]: https://leetcode.com/problems/implement-strstr
+[src]: https://github.com/andavid/leetcode-java/blob/master/src/com/andavid/leetcode/_028/Solution.java

src/com/andavid/leetcode/_028/Solution.java

@@ -0,0 +1,13 @@
+class Solution {
+  public int strStr(String haystack, String needle) {
+    if (null == haystack || null == needle) {
+      return -1;
+    }
+    return haystack.indexOf(needle);
+  }
+
+  public static void main(String[] args) {
+    Solution solution = new Solution();
+    System.out.println(solution.strStr("hello", "ll"));
+  }
+}