Add comprehensive LeetCode solutions index documentation

src/exercises/20.valid-parentheses.py

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+from string import *
+from re import *
+from datetime import *
+from collections import *
+from heapq import *
+from bisect import *
+from copy import *
+from math import *
+from random import *
+from statistics import *
+from itertools import *
+from functools import *
+from operator import *
+from io import *
+from sys import *
+from json import *
+from builtins import *
+import string
+import re
+import datetime
+import collections
+import heapq
+import bisect
+import copy
+import math
+import random
+import statistics
+import itertools
+import functools
+import operator
+import io
+import sys
+import json
+from typing import *
+
+
+# @leet start
+class Solution:
+    def isValid(self, s: str) -> bool:
+        if len(s) < 2:
+            return False
+        valid = {"]": "[", ")": "(", "}": "{"}
+        arr = []
+        for i in range(len(s)):
+            if s[i] in valid:
+                if len(arr) == 0:
+                    return False
+                if arr[len(arr) - 1] != valid[s[i]]:
+                    return False
+                arr.pop()
+            else:
+                arr.append(s[i])
+        return len(arr) == 0
+
+
+# @leet end
+