题解 | #删除字符串中出现次数最少的字符#

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

/**
 * 【删除字符串中出现次数最少的字符】
 *
 *  描述：实现删除字符串中出现次数最少的字符，若出现次数最少的字符有多个，则把出现次数最少的字符都删除。
 *  输出删除这些单词后的字符串，字符串中其它字符保持原来的顺序。
 *
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String nextLine = sc.nextLine();
        
        char[] chars = nextLine.toCharArray();
		// map记录每个字符出现的次数
        HashMap<Character, Integer> hashMap = new HashMap<>();
        for (int i = 0; i < chars.length; i++) {
            if (hashMap.containsKey(chars[i])) {
                hashMap.put(chars[i], hashMap.get(chars[i]) + 1);
            } else {
                hashMap.put(chars[i], 1);
            }
        }
		
      StringBuilder sb = new StringBuilder(nextLine);
        for (int i = chars.length - 1; i >= 0; i--) {
            if (isMinShow(chars[i], hashMap)) {
                sb.deleteCharAt(i);
            }
        }
        System.out.println(sb);
    }

    /**
     * 判断字符是否出现次数最少
     *
     * @param targetChar  目标字符
     * @param hashMap      
     * @return
     */
    public static boolean isMinShow(char targetChar, HashMap<Character, Integer> hashMap) {
        int min = hashMap.get(targetChar);
        int count = min;

        Set<Map.Entry<Character, Integer>> entrySet = hashMap.entrySet();
        for (Map.Entry<Character, Integer> entry : entrySet) {
            min = Math.min(min, entry.getValue());
        }
        return count == min;
    }
}