/**
1. 先把段落中的单词划分出来并转换为小写
2. 统计所有单词的频率
3. 把ban-list中单词频率置为-1
4. 遍历所有单词, 输出频率最高的
*/

class Solution {
    public String mostCommonWord(String paragraph, String[] banned) {
        Map<String, Integer> freq = new TreeMap<>();
        List<String> slice = wordBreak(paragraph);

        for (int i = 0; i < slice.size() ; i ++){
            String word = slice.get(i);
            if (freq.get(word) == null) freq.put(word, 0);
            freq.put(word, freq.get(word) + 1);
        }

        for (int i = 0; i < banned.length;  i++){
            freq.remove(banned[i]);
        }

        int maxFreq = 0;
        String res = null;
        for (String word : freq.keySet()){
            if (freq.get(word) > maxFreq){
                res = word;
                maxFreq = freq.get(word);
            }
        }
        return res;
    }

    public List<String> wordBreak(String paragraph){
        List<String> slices = new ArrayList<>();
        StringBuilder buffer = new StringBuilder();
        for (int i = 0 ; i < paragraph.length(); i++){
            char c = paragraph.charAt(i);
            if ('a' <= c && c <= 'z' ||  'A' <= c && c <= 'Z'){
                buffer.append(c);
            } else if (buffer.length() != 0){
                slices.add(buffer.toString().toLowerCase());
                buffer.setLength(0);
            }
        }
        if (buffer.length() != 0) slices.add(buffer.toString().toLowerCase());
        return slices;
    }

}