题解 | #删除字符串中出现次数最少的字符#

/*
 * 解题思路: 统计字符出现的次数, 然后排序, 可以考虑用TreeMap
 * 补充说明: 该题选用的当前数据结构性能较差, 可将TreeMap换成HashMap, 将ArrayList换成Stack或LinkedList (换了好像性能更差了)
 */
import java.util.*;

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

        while (sc.hasNextLine()) {
            TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
            String str = sc.nextLine();
            for (int i = 0; i < str.length(); i++) {
                int key = str.charAt(i);
                int value = (map.containsKey(key) ? map.get(key) + 1 : 1);
                map.put(key, value);
            }

            ArrayList<Map.Entry<Integer, Integer>> list = new ArrayList<Map.Entry<Integer, Integer>>(map.entrySet());
            Collections.sort(list, new Comparator<Map.Entry<Integer, Integer>>() {
                public int compare(Map.Entry<Integer, Integer> o1, Map.Entry<Integer, Integer> o2) {
                    return o1.getValue() - o2.getValue();
                }
            });

            Map.Entry<Integer, Integer> entry = list.remove(0);
            int min = entry.getValue();
            String res = str.replace((char)entry.getKey().intValue() + "", "");

            while (!list.isEmpty()) {
                entry = list.remove(0);
                if (entry.getValue() > min) {
                    break;
                }
                res = res.replace((char)entry.getKey().intValue() + "", "");
            }
            System.out.println(res);
        }
    }
}