15、 ... and 、 The most common word

15.1、 Question design requirements

   Given a paragraph (paragraph) And a list of forbidden words (banned). Return the most times , Words that are not in the disable list at the same time .

   The title guarantees that at least one word is not in the forbidden list , And the only answer is .

   Words in the disable list are represented in lowercase letters , No punctuation . Words in paragraphs are not case sensitive . The answers are in small letters .

 Example ：
 Input : 
paragraph = "Bob hit a ball, the hit BALL flew far after it was hit."
banned = ["hit"]
 Output : "ball"
 explain : 
"hit"  There is 3 Time , But it's a forbidden word .
"ball"  There is 2 Time  ( At the same time, no other words appear 2 Time ), So it's the most frequent one in the paragraph , Words that are not in the disable list . 
 Be careful , All these words are case insensitive in paragraphs , Punctuation needs to be ignored （ Even if it's next to a word, ignore ,  such as  "ball,"）, 
"hit" Not the final answer , Although it appears more often , But it's in the list of forbidden words .

 Tips ：
1 <=  Paragraph length  <= 1000
0 <=  Disable several words  <= 100
1 <=  Disable word length  <= 10
 The answer is only ,  And they're all small letters  ( Even in  paragraph  It's in capitals , Even some specific nouns , The answers are in lowercase .)
paragraph  Letters only 、 Spaces and the following punctuation !?',;.
 There are no words without or with hyphens .
 Words contain only letters , There will be no ellipsis or other punctuation marks .

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/most-common-word

15.2、 Their thinking

   First remove the symbol from the string , Then count the number of words in the string , Then remove the forbidden words , Remove the words after the forbidden words map The word output of the number of occurrences can .

15.3、 Algorithm

// Remove the symbol from the string 
String [] str = paragraph.split(" |\\!|\\?|'|\\;|\\.|,");
Map<String,Integer> map = new HashMap<>();
// Count the number of occurrences of words in the string 
for (int i = 0; i < str.length; i++) {
    
    // Will array b Remove the space in the 
    if (str[i].length()==0){
    
        continue;
    }
    // Convert letters to lowercase letters 
    str[i] = str[i].toLowerCase();
    // to map assignment ,str[i] by map Medium key,value Then it increases in order 
    //getOrDefault() The function is used in map Get passed in from key Of value, If not, that is value If it is empty , Returns the value of the passed in parameter 
    // In this case , If value It's empty , Initial value Then for 1; If value Not empty , Then return to key Corresponding value One more 
    map.put(str[i],map.getOrDefault(str[i],0)+1);
}
// take ban Disabled words in map Removing the 
for(int i=0;i<banned.length;i++){
    
    map.remove(banned[i]);
}
String ans=" ";
// Take out map Compare and replace the numbers in 
for(String s:map.keySet()){
    
    // take map Middle string s Of value And getOrDefault( Quite successful , Increasing ) Compare 
    if(map.get(s)>map.getOrDefault(ans,0)){
    
        ans=s;
    }
}
return ans;