题解 | #计算某字符出现次数#

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.nextLine().toLowerCase();
        char[] chars = s.toCharArray();

        String s1 = scanner.nextLine().toLowerCase();
        char[] chars1 = s1.toCharArray();
        char myChar = chars1[0];

        Map<Character, Integer> map = new HashMap<>(chars.length);
        for (char aChar : chars) {
            Integer count = map.get(aChar);
            if (count == null) {
                map.put(aChar, 1);
            } else {
                map.put(aChar, ++count);
            }
        }

        Integer integer = map.get(myChar);
        System.out.println(null == integer ? 0 : integer);
    }
}