Leetcode - most-common-word

https://leetcode.com/problems/most-common-word/

Given a paragraph and a list of banned words, return the most frequent word that is not in the list of banned words.  It is guaranteed there is at least one word that isn't banned, and that the answer is unique.

Words in the list of banned words are given in lowercase, and free of punctuation.  Words in the paragraph are not case sensitive.  The answer is in lowercase.

Example:

Input: 
paragraph = "Bob hit a ball, the hit BALL flew far after it was hit."
banned = ["hit"]
Output: "ball"
Explanation: 
"hit" occurs 3 times, but it is a banned word.
"ball" occurs twice (and no other word does), so it is the most frequent non-banned word in the paragraph. 
Note that words in the paragraph are not case sensitive,
that punctuation is ignored (even if adjacent to words, such as "ball,"), 
and that "hit" isn't the answer even though it occurs more because it is banned.

Use a map to count every word's frequency.

func mostCommonWord(paragraph string, banned []string) string {
    
    paragraph = strings.ToLower(paragraph)
    para := []byte{}
    for i := 0; i < len(paragraph); i++ {
        if isSymbol(paragraph[i]) {
            para = append(para, ' ')
        } else {
            para = append(para, paragraph[i])
        }
    }
    paragraph = string(para)
    paras := strings.Split(paragraph, " ")
    
    maxWord := ""
    maxCount := 0
    countMap := map[string]int{}
    bannedMap := map[string]bool{}
    for _, b := range banned{
        bannedMap[b] = true
    }
    for i := 0; i < len(paras); i++ {
        if !bannedMap[paras[i]] && paras[i] != "" { 
            countMap[paras[i]]++
        }
    }
    for key, val := range countMap {
        if maxCount < val {
            maxCount = val
            maxWord = key
        }
    }
    
    return maxWord
}

func isSymbol(b byte) bool {
    symbols := "!?',;."
    for i := 0; i < len(symbols); i++ {
        if symbols[i] == b {
            return true
        }
    }
    return false
}

def most_common_word(paragraph, banned)
    paragraph.downcase!
    paragraph.tr!("!?',;.", " ")
    paras = paragraph.split(" ")
    banned_hash = {}
    banned.each {|b| banned_hash[b] = true}
    hash = {}
   
    paras.each do |p|
        hash[p] = 0 if hash[p].nil?
        hash[p] += 1 if !banned_hash[p]
    end
    
    max_count = 0
    max_word = ""
    
    hash.each do |key, val|
        if val > max_count
            max_count = val
            max_word = key
        end
    end

    return max_word
end

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