refactor(work): restructure solution directories with bucket level and add .gitkeep placeholders

work/1/Easy/String/20.valid-parentheses.py

@@ -0,0 +1,76 @@
+"""
+20. Valid Parentheses
+Difficulty: Easy
+https://leetcode.com/problems/valid-parentheses/
+
+──────────────────────────────────────────────────
+
+Given a string s containing just the characters '(', ')', '{', '}',
+'[' and ']', determine if the input string is valid.
+
+An input string is valid if:
+
+        • Open brackets must be closed by the same type of brackets.
+
+        • Open brackets must be closed in the correct order.
+
+• Every close bracket has a corresponding open bracket of the same
+type.
+
+
+
+Example 1:
+
+Input: s = "()"
+
+Output: true
+
+Example 2:
+
+Input: s = "()[]{}"
+
+Output: true
+
+Example 3:
+
+Input: s = "(]"
+
+Output: false
+
+Example 4:
+
+Input: s = "([])"
+
+Output: true
+
+Example 5:
+
+Input: s = "([)]"
+
+Output: false
+
+
+
+Constraints:
+
+        • 1 <= s.length <= 10^4
+
+        • s consists of parentheses only '()[]{}'.
+"""
+
+
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = []
+        pairs = {")": "(", "]": "[", "}": "{"}
+
+        for c in s:
+            if c in pairs:
+                if stack and pairs[c] == stack[-1]:
+                    stack.pop()
+                else:
+                    return False
+            else:
+                stack.append(c)
+
+        return True if not stack else False