Create 28-Implement-strStr.py

Author: neetcode-gh

28-Implement-strStr.py

@@ -0,0 +1,30 @@
+class Solution:
+    def strStr(self, haystack: str, needle: str) -> int:
+        if needle == "": return 0
+        lps = [0] * len(needle)
+        
+        prevLPS, i = 0, 1
+        while i < len(needle):
+            if needle[i] == needle[prevLPS]:
+                lps[i] = prevLPS + 1
+                prevLPS += 1
+                i += 1
+            elif prevLPS == 0:
+                lps[i] = 0
+                i += 1
+            else:
+                prevLPS = lps[prevLPS - 1]
+        
+        i = 0 # ptr for haystack
+        j = 0 # ptr for needle
+        while i < len(haystack):
+            if haystack[i] == needle[j]:
+                i, j = i + 1, j + 1
+            else:
+                if j == 0:
+                    i += 1
+                else:
+                    j = lps[j - 1]
+            if j == len(needle):
+                return i - len(needle)
+        return -1