Add solution 028 [Java]

Author: yanglbme

README.md

@@ -26,6 +26,7 @@ Complete [solutions](https://github.com/doocs/leetcode/tree/master/solution) to
 | 014 | [Longest Common Prefix](https://github.com/doocs/leetcode/tree/master/solution/014.Longest%20Common%20Prefix) | `String` |
 | 020 | [Valid Parentheses](https://github.com/doocs/leetcode/tree/master/solution/020.Valid%20Parentheses) | `String`, `Stack` |
 | 021 | [Merge Two Sorted Lists](https://github.com/doocs/leetcode/tree/master/solution/021.Merge%20Two%20Sorted%20Lists) | `Linked List` |
+| 028 | [Implement strStr()](https://github.com/doocs/leetcode/tree/master/solution/028.Implement%20strStr()) | `Two Pointers`, `String` |
 | 053 | [Maximum Subarray](https://github.com/doocs/leetcode/tree/master/solution/053.Maximum%20Subarray) | `Array`, `Divide and Conquer`, `Dynamic Programming` |
 | 070 | [Climbing Stairs](https://github.com/doocs/leetcode/tree/master/solution/070.Climbing%20Stairs) | `Dynamic Programming` |
 | 083 | [Remove Duplicates from Sorted List](https://github.com/doocs/leetcode/tree/master/solution/083.Remove%20Duplicates%20from%20Sorted%20List) | `Linked List` |
@@ -88,6 +89,8 @@ I'm looking for long-term contributors/partners to this repo! Send me [PRs](http
 
 ## Contributors
 
+" If you want to go fast, go alone. If you want to go far, go together. And that's the spirit of [teamwork](https://github.com/doocs/leetcode/graphs/contributors) ".
+
 <!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
 | <center> [<img src="https://avatars3.githubusercontent.com/u/21008209?v=4" width="80px;"/>](https://github.com/yanglbme)<br />[💻](https://github.com/doocs/leetcode/commits?author=yanglbme "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/23625436?v=4" width="80px;"/>](https://github.com/chakyam)<br />[💻](https://github.com/doocs/leetcode/commits?author=chakyam "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/10081554?v=4" width="80px;"/>](https://github.com/zhkmxx9302013)<br />[💻](https://github.com/doocs/leetcode/commits?author=zhkmxx9302013 "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/40383345?v=4" width="80px;"/>](https://github.com/MarkKuang1991)<br />[💻](https://github.com/doocs/leetcode/commits?author=MarkKuang1991 "Code") </center> | <center> [<img src="https://avatars3.githubusercontent.com/u/12371194?v=4" width="80px;"/>](https://github.com/fonxian)<br />[💻](https://github.com/doocs/leetcode/commits?author=fonxian "Code") </center> | 
 |---|---|---|--|--|

solution/028.Implement strStr()/README.md

@@ -0,0 +1,59 @@
+## 实现strStr()
+### 题目描述
+
+实现 [strStr()](https://baike.baidu.com/item/strstr/811469) 函数。
+
+给定一个 haystack 字符串和一个 needle 字符串，在 haystack 字符串中找出 needle 字符串出现的第一个位置 (从0开始)。如果不存在，则返回  -1。
+
+**示例 1:**
+```
+输入: haystack = "hello", needle = "ll"
+输出: 2
+```
+
+**示例 2:**
+```
+输入: haystack = "aaaaa", needle = "bba"
+输出: -1
+```
+
+**说明:**
+
+当 `needle` 是空字符串时，我们应当返回什么值呢？这是一个在面试中很好的问题。
+
+对于本题而言，当 `needle` 是空字符串时我们应当返回 0 。这与C语言的 [strstr()](https://baike.baidu.com/item/strstr/811469) 以及 Java的 `indexOf()` 定义相符。
+
+### 解法
+遍历 `haystack` 和 `needle`，利用指针 `p`, `q` 分别指向这两个字符串。对于每一个位置对于的字符，如果两字符相等，继续判断下一个位置的字符是否相等；否则 `q` 置为 0，`p` 置为最初匹配的字符的下一个位置，即 `p - q + 1`。
+
+```java
+class Solution {
+    public int strStr(String haystack, String needle) {
+        if ("".equals(needle)) {
+            return 0;
+        }
+        
+        int len1 = haystack.length();
+        int len2 = needle.length();
+        int p = 0;
+        int q = 0;
+        while (p < len1) {
+            if (haystack.charAt(p) == needle.charAt(q)) {
+                if (len2 == 1) {
+                    return p;
+                }
+                ++p;
+                ++q;
+            } else {
+                p -= q - 1;
+                q = 0;
+            }
+            
+            if (q == len2) {
+                return p - q;
+            }
+        }
+        return -1;
+    }
+}
+```

solution/028.Implement strStr()/Solution.java

@@ -0,0 +1,29 @@
+class Solution {
+    public int strStr(String haystack, String needle) {
+        if ("".equals(needle)) {
+            return 0;
+        }
+
+        int len1 = haystack.length();
+        int len2 = needle.length();
+        int p = 0;
+        int q = 0;
+        while (p < len1) {
+            if (haystack.charAt(p) == needle.charAt(q)) {
+                if (len2 == 1) {
+                    return p;
+                }
+                ++p;
+                ++q;
+            } else {
+                p -= q - 1;
+                q = 0;
+            }
+
+            if (q == len2) {
+                return p - q;
+            }
+        }
+        return -1;
+    }
+}