寻找第一个出现次数最少的字符

同理寻找第一个出现次数最少的字符，一次循环的还没想好

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

/**
 * Created by zfr on 2018/08/05.
 * 寻找第一个出现次数最少的字符 
 */
public class Solution {
    public static void main(String[] args) {
            // TODO Auto-generated method stub
        Solution  a = new  Solution ();
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        if(str == null || str.length() == 0 ){
            System.out.println("输入有误！");
            return;
        }
        System.out.println(a.cal1(str));
        System.out.println(a.cal2(str));
    }
    ///三次循环
    private char cal1(String str) {
        Map<Character,Integer> map = new HashMap<>();
        char[] ch = str.toCharArray();
        for (int i = 0;i<ch.length;i++) {
            if(map.containsKey(ch[i])){
                map.put(ch[i],map.get(ch[i])+1);
            }else {
                map.put(ch[i],1);
            }
        }
        int count = Integer.MAX_VALUE;
        for (Map.Entry<Character,Integer> entry:map.entrySet()) {
            count = Math.min(count,entry.getValue());
        }
        for(char c : ch){
            if(map.get(c) == count ){
                return c ;
            }
        }
        return ch[0];
    }
    //两次循环
    private char cal2(String str) {
        Map<Character,Integer> map = new HashMap<>();
        char[] ch = str.toCharArray();
        for (int i = 0;i<ch.length;i++) {
            if(map.containsKey(ch[i])){
                map.put(ch[i],map.get(ch[i])+1);
            }else {
                map.put(ch[i],1);
            }
        }
        int index = Integer.MAX_VALUE ;
        char minChar = ch[0];
        for(int i = 0 ;i<ch.length;i++){
            if(map.get(ch[i]) < index ){
                index = map.get(ch[i]);
                minChar = ch[i] ;
            }
        }
        return minChar;
    }

}