solve problem Implement Strstr

Author: P-ppc

README.md

@@ -178,6 +178,7 @@ All solutions will be accepted!
 |643|[Maximum Average Subarray I](https://leetcode-cn.com/problems/maximum-average-subarray-i/description/)|[java/py/js](./algorithms/MaximumAverageSubarrayI)|Easy|
 |189|[Rotate Array](https://leetcode-cn.com/problems/rotate-array/description/)|[java/py/js](./algorithms/RotateArray)|Easy|
 |687|[Longest Univalue Path](https://leetcode-cn.com/problems/longest-univalue-path/description/)|[java/py/js](./algorithms/LongestUnivaluePath)|Easy|
+|28|[Implement Strstr](https://leetcode-cn.com/problems/implement-strstr/description/)|[java/py/js](./algorithms/ImplementStrstr)|Easy|
 
 # Database
 |#|Title|Solution|Difficulty|

algorithms/ImplementStrstr/README.md

@@ -0,0 +1,2 @@
+# Implement Strstr
+For performance we can use KMP to solve this problem

algorithms/ImplementStrstr/Solution.java

@@ -0,0 +1,37 @@
+class Solution {
+    public int strStr(String haystack, String needle) {
+        int needleLength = needle.length();
+        if (needleLength == 0) return 0;
+        
+        int i = 0, j = 0;
+        List<Integer> next = new ArrayList<Integer>();
+        
+        while (i < needleLength) {
+            if (i == 0 || (needle.charAt(i) != needle.charAt(j) && j == 0)) {
+                next.add(0);
+            } else if (needle.charAt(i) == needle.charAt(j)) {
+                next.add(j + 1);
+                j++;
+            } else if (needle.charAt(i) != needle.charAt(j)) {
+                j = next.get(j - 1);
+                continue;
+            }
+            i++;
+        }
+        
+        i = j = 0;
+        
+        while (i < haystack.length() && j < needleLength) {
+            if (haystack.charAt(i) == needle.charAt(j)) {
+                i++;
+                j++;
+            } else if (j == 0) {
+                i++;
+            } else {
+                j = next.get(j - 1);
+            }
+        }
+        
+        return j == needleLength ? i - j : -1;
+    }
+}

algorithms/ImplementStrstr/solution.js

@@ -0,0 +1,38 @@
+/**
+ * @param {string} haystack
+ * @param {string} needle
+ * @return {number}
+ */
+var strStr = function(haystack, needle) {
+    if (needle === '') return 0
+    
+    let next = [],
+        i = j = 0
+    
+    while (i < needle.length) {
+        if (i === 0 || (needle[i] !== needle[j] && j === 0)) {
+            next.push(0)
+        } else if (needle[i] === needle[j]) {
+            next.push(j + 1)
+            j++
+        } else if (needle[i] !== needle[j]) {
+            j = next[j - 1]
+            continue
+        }
+        i++
+    }
+    i = j = 0
+    
+    while (i < haystack.length && j < needle.length) {
+        if (haystack[i] == needle[j]) {
+            i++
+            j++
+        } else if (j === 0) {
+            i++
+        } else {
+            j = next[j - 1]
+        }
+    }
+    
+    return j === needle.length ? i - j : -1
+};

algorithms/ImplementStrstr/solution.py

@@ -0,0 +1,36 @@
+class Solution(object):
+    def strStr(self, haystack, needle):
+        """
+        :type haystack: str
+        :type needle: str
+        :rtype: int
+        """
+        if needle == '':
+            return 0
+    
+        nxt = []
+        i = j = 0
+        
+        while i < len(needle):
+            if i == 0 or (needle[i] != needle[j] and j == 0):
+                nxt.append(0)
+            elif needle[i] == needle[j]:
+                nxt.append(j + 1)
+                j += 1
+            elif needle[i] != needle[j] and j > 0:
+                j = nxt[j - 1]
+                continue
+            i += 1
+        
+        i = j = 0
+        
+        while i < len(haystack) and j < len(needle):
+            if haystack[i] == needle[j]:
+                i += 1
+                j += 1
+            elif j == 0:
+                i += 1
+            else:
+                j = nxt[j - 1]
+        
+        return i - j if j == len(needle) else -1