HashMap 解决计算字符个数问题

用了hashmap来做。当然还是推荐(str.length()-str.replaceAll(s,"").length()

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String input = sc.next();        
        String upperStr = input.toUpperCase();

        char c = sc.next().toUpperCase().charAt(0);

        int ans = checkNum(upperStr, c);

        System.out.print(ans);
    }

    private static int checkNum(String str, char c){
        int res = 0;

        int len = str.length();
        HashMap<Character, Integer> map= new HashMap<> ();
        for(int i = 0; i < len; i++){
            char cur = str.charAt(i);
            map.put(cur, map.getOrDefault(cur, 0)+1);
        }

        if(!map.containsKey(c)){
            return res;
        } else {
            res = map.get(c);
            return res;
        }
    }
}