409: Solution with step by step explanation
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n1. Initialize an empty dictionary freq_dict to store the frequency of eac
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n1. Initialize an empty dictionary freq_dict to store the frequency of each character in the string s.\n2. Iterate over each character char in the string s and add it to the dictionary freq_dict if it doesn\'t exist, or increment its frequency by 1 if it does.\n3. Initialize a variable length to 0, which will store the length of the longest palindrome.\n4. Iterate over each frequency freq in the values of the dictionary freq_dict and add up the length of all even-frequency characters by computing freq // 2 * 2 and adding it to the variable length.\n5. Check if there are any characters whose frequency is odd by using the any function on a generator expression that checks if the frequency is odd (freq % 2 == 1). If there are any such characters, add one of them to the length by incrementing length by 1.\n6. Return the variable length as the answer.\n\nThe algorithm works by observing that any palindrome can be constructed by pairing up characters with even frequencies, and adding a single character with an odd frequency if one exists. By iterating over the frequencies of each character and adding up the length of all even-frequency characters, and then adding one odd-frequency character (if any exist), we obtain the length of the longest possible palindrome that can be constructed from the characters in the input string.\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution:\n    def longestPalindrome(self, s: str) -> int:\n        # Initialize a dictionary to store the frequency of each character in the string\n        freq_dict = {}\n        for char in s:\n            freq_dict[char] = freq_dict.get(char, 0) + 1\n        \n        # Initialize a variable \'length\' to 0, which will store the length of the longest palindrome\n        length = 0\n        \n        # Iterate through the dictionary and add up the length of all even-frequency characters\n        for freq in freq_dict.values():\n            length += freq // 2 * 2\n        \n        # Check if there are any characters whose frequency is odd. If yes, add one of them to the length\n        if any(freq % 2 == 1 for freq in freq_dict.values()):\n            length += 1\n        \n        # Return the length as the answer\n        return length\n\n```
['Hash Table', 'String', 'Greedy', 'Python', 'Python3']