feat(strings): first occurrence

Author: BrianLusina

pystrings/first_occurrence/README.md

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+# Find the Index of the First Occurrence in a String
+
+Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle
+is not part of haystack.
+
+```text
+Example 1:
+
+Input: haystack = "sadbutsad", needle = "sad"
+Output: 0
+Explanation: "sad" occurs at index 0 and 6.
+The first occurrence is at index 0, so we return 0.
+```
+
+```text
+Example 2:
+
+Input: haystack = "leetcode", needle = "leeto"
+Output: -1
+Explanation: "leeto" did not occur in "leetcode", so we return -1.
+```
+
+## Related Topics
+
+- Two pointers
+- String
+- String Matching

pystrings/first_occurrence/__init__.py

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+from utils.benchmark import func_timer
+
+
+@func_timer
+def str_str(haystack: str, needle: str) -> int:
+    # makes sure we don't iterate through a substring that is shorter than needle
+    for i in range(len(haystack) - len(needle) + 1):
+        # check if any substring of haystack with the same length as needle is equal to needle
+        if haystack[i: i + len(needle)] == needle:
+            # if yes, we return the first index of that substring
+            return i
+    # if we exit the loop, return -1
+    return -1

pystrings/first_occurrence/test_first_occurrence.py

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+import unittest
+from . import str_str
+
+
+class StrStrTestCase(unittest.TestCase):
+    def test_sadbutsad_sad(self):
+        """sadbutsad, needle = sad"""
+        haystack = "sadbutsad"
+        needle = "sad"
+        expected = 0
+        actual = str_str(haystack, needle)
+
+        self.assertEqual(expected, actual)
+
+    def test_leetcode_leeto(self):
+        """leetcode, needle = leeto"""
+        haystack = "leetcode"
+        needle = "leeto"
+        expected = -1
+        actual = str_str(haystack, needle)
+
+        self.assertEqual(expected, actual)
+
+
+if __name__ == '__main__':
+    unittest.main()

utils/benchmark/__init__.py

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+from .timer import func_timer
+
+__all__ = [
+    "func_timer"
+]

utils/benchmark/timer.py

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+from typing import Callable
+import time
+
+
+def func_timer(func: Callable) -> Callable:
+    """
+    Decorator function that times the execution of a function
+    @param func: Function to time
+    @return: Callable that wraps around the function to time
+    """
+
+    def timer(*args, **kwargs):
+        """
+        Times a given function and passes in the arguments called on the function
+        @param args:
+        @param kwargs:
+        @return:
+        """
+        start = time.time()
+        value = func(*args, **kwargs)
+        end = time.time()
+        runtime = end - start
+        msg = "{func} took {time} seconds to complete its execution."
+        print(msg.format(func=func.__name__, time=runtime))
+        return value
+
+    return timer