Add 28

Author: varvarvarvar

README.md

@@ -15,6 +15,7 @@ Solutions for https://leetcode.com/ algorithmic problems.
 | [Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [0020](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0020.py) |
 | [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [0026](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0026.py) |
 | [Remove Element](https://leetcode.com/problems/remove-element/) | [0027](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0027.py) |
+| [Implement strStr()](https://leetcode.com/problems/implement-strstr/) | [0028](https://github.com/varvarvarvar/leetcode/blob/master/solutions/0028.py) |
 | [Sort Colors](https://leetcode.com/problems/sort-colors/) | [0075](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0075.py) |
 | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)  | [0125](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0125.py)  |
 | [Rotate Array](https://leetcode.com/problems/rotate-array/)  | [0189](https://github.com/varvara-krasavina/leetcode/blob/master/solutions/0189.py) |

solutions/0028.py

@@ -0,0 +1,55 @@
+"""Return the index of the first occurrence of needle in haystack,
+or -1 if needle is not part of haystack.
+
+For the purpose of this problem, we will return 0 when needle is an empty string.
+
+"""
+
+
+class Solution:
+    def strStr(self, haystack: str, needle: str) -> int:
+
+        if not needle:
+            return 0
+
+        if len(needle) > len(haystack):
+            return -1
+
+        if len(needle) == len(haystack):
+            if needle == haystack:
+                return 0
+            return -1
+
+        for i in range(len(haystack) - len(needle) + 1):
+
+            first_j = i
+
+            for j in range(len(needle)):
+
+                if first_j == len(haystack):
+                    break
+
+                if haystack[first_j] != needle[j]:
+                    break
+
+                first_j += 1
+
+                if first_j - i == len(needle):
+                    return i
+
+        return -1
+
+
+if __name__ == "__main__":
+
+    sol = Solution()
+
+    assert sol.strStr("aaa", "aaaa") == -1
+    assert sol.strStr("mississippi", "issip") == 4
+    assert sol.strStr("hello", "ll") == 2
+    assert sol.strStr("aaa", "aaa") == 0
+    assert sol.strStr("a", "a") == 0
+    assert sol.strStr("aaa", "aaa") == 0
+    assert sol.strStr("ba", "a") == 1
+    assert sol.strStr("aaaaa", "bba") == -1
+    assert sol.strStr("", "") == 0