added leetcode questions

14. Questions/leetcode 28 - index of first occurrence.py

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+# find the index of the first occurrence of a string | leetcode 28 | https://leetcode.com/problems/find-the-index-of-the-first-occurrence-in-a-string/
+# sliding window to match each character of the haystack with the needle; no slices.
+
+class Solution:
+    def strStr(self, haystack: str, needle: str) -> int:
+        # ----- using regex -----
+        # if needle == '':
+        #     return 0
+
+        # import re
+        # match = re.search(needle, haystack)
+        # return match.start() if match else -1
+
+        # ----- using sliding windows -----
+        ptrL, ptrR = 0, 0
+        N_needle, N_haystack = len(needle), len(haystack)
+        while ptrR < N_haystack:
+            if haystack[ptrR] == needle[ptrR - ptrL]:
+                ptrR += 1
+                if ptrR - ptrL > N_needle - 1:
+                    return ptrL
+            else:
+                ptrR = ptrL + 1
+                ptrL += 1
+
+        return -1

14. Questions/leetcode 443 - string compression.py

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+# string compression | leetcode 443 | https://leetcode.com/problems/string-compression/
+# sliding window to keep track of a char's occurence
+
+class Solution:
+    def compress(self, chars: list[str]) -> int:
+        ptrL, ptrR = 0, 0
+        total = 0
+        chars += " "
+
+        while ptrR < len(chars):
+            if chars[ptrL] != chars[ptrR]:
+                chars[total] = chars[ptrL]
+                total += 1
+                group = ptrR - ptrL
+                if group > 1:
+                    for x in str(group):
+                        chars[total] = x
+                        total += 1
+                ptrL = ptrR
+            ptrR += 1
+
+        return total