Update README.md

Add KMP for Problem 28.

Author: qiyuangong

README.md

@@ -1,7 +1,13 @@
-# My Python Solution for Leetcode
+# My Python Solutions for Leetcode
 
+[The whole lists](https://github.com/qiyuangong/leetcode/tree/master/python):
 
 | # | Title | Solution | Basic idea (One line) |
 |---| ----- | -------- | ---------- |
-| 1 | [Two Sum](https://leetcode.com/problems/two-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1_Two_Sum.py) | 1. hash 2. Sort and search with two point|
-| 15 | [3Sum](https://leetcode.com/problems/3sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/15_3Sum.py) | 1. Sort and O(n) search with three points 2. Multiple Two Sum (Problem 1) |
+| 1 | [Two Sum](https://leetcode.com/problems/two-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/1_Two_Sum.py) | 1. hash 2. Sort and search with two points|
+| 15 | [3Sum](https://leetcode.com/problems/3sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/15_3Sum.py) | 1. Sort and O(n^2) search with three points 2. Multiple Two Sum (Problem 1) |
+| 16 | [3Sum Closest](https://leetcode.com/problems/3sum-closest/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/16_3Sum_Closest.py) | Sort and Multiple Two Sum check abs|
+| 18 | [4Sum](https://leetcode.com/problems/4sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/18_4Sum.py) | The same as 3Sum, but we can merge pairs with the same sum |
+| 28 | [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/28_Implement_strStr().py) | 1. O(nm) comparison 2. KMP|
+| 125 | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/125_Valid_Palindrome.py)| Exclude non-alphanumeric characters and compare O(n) |
+||

python/28_Implement_strStr().py

@@ -1,26 +1,26 @@
 class Solution(object):
-    def strStr(self, haystack, needle):
-        """
-        :type haystack: str
-        :type needle: str
-        :rtype: int
-        """
-        lsh, lsn = len(haystack), len(needle)
-        if lsn == 0:
-            return 0
-        pos, index = 0, 0
-        while index <= lsh - lsn:
-            if haystack[index] == needle[pos]:
-                backup = index
-                while index < lsh and pos < lsn and haystack[index] == needle[pos]:
-                    pos += 1
-                    index += 1
-                if pos == len(needle):
-                    return index - pos
-                index = backup
-            index += 1
-            pos = 0
-        return -1
+    # def strStr(self, haystack, needle):
+    #     """
+    #     :type haystack: str
+    #     :type needle: str
+    #     :rtype: int
+    #     """
+    #     lsh, lsn = len(haystack), len(needle)
+    #     if lsn == 0:
+    #         return 0
+    #     pos, index = 0, 0
+    #     while index <= lsh - lsn:
+    #         if haystack[index] == needle[pos]:
+    #             backup = index
+    #             while index < lsh and pos < lsn and haystack[index] == needle[pos]:
+    #                 pos += 1
+    #                 index += 1
+    #             if pos == len(needle):
+    #                 return index - pos
+    #             index = backup
+    #         index += 1
+    #         pos = 0
+    #     return -1
 
     # def strStr(self, haystack, needle):
     #     lsh, lsn = len(haystack), len(needle)
@@ -34,3 +34,37 @@ def strStr(self, haystack, needle):
     #                 return index
     #         index += 1
     #     return -1
+
+    # KMP
+    # https://discuss.leetcode.com/topic/3576/accepted-kmp-solution-in-java-for-reference/2
+    def strStr(self, haystack, needle):
+        lsh, lsn = len(haystack), len(needle)
+        if lsn == 0:
+            return 0
+        next = self.makeNext(needle)
+        i = j = 0
+        while i < lsh:
+            if j == -1 or haystack[i] == needle[j]:
+                i += 1
+                j += 1
+                if j == lsn:
+                    return i - lsn
+            if i < lsh and haystack[i] != needle[j]:
+                j = next[j]
+        return -1
+
+    def makeNext(self, needle):
+        ls = len(needle)
+        next = [0] * ls
+        next[0], i, j = -1, 0, -1
+        while i < ls - 1:
+            if j == -1 or needle[i] == needle[j]:
+                next[i + 1] = j + 1
+                if needle[i + 1] == needle[j + 1]:
+                    next[i + 1] = next[j + 1]
+                i += 1
+                j += 1
+            if needle[i] != needle[j]:
+                j = next[j]
+        return next
+