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Determine if a string containing parentheses is valid. A valid string has matching and properly nested opening and closing parentheses.
#1. Valid Parentheses
You're given daily stock prices. Find the maximum profit you can make by buying and selling the stock once. You must buy before you sell.
#2. Best Time to Buy and Sell Stock
Determine if a given string is a palindrome, considering only alphanumeric characters and ignoring cases. Essentially, check if the string reads the same forwards and backward after removing non-alphanumeric characters and converting to lowercase.
#3. Valid Palindrome