一个字符串中可能包含a~z中的多个字符，如有重复，如String data="aavzcadfdsfsdhshgWasdfasdf"，求出现次数最多的那个字母及次数，如有多个重复的则都求出。

最近在《JAVA程序员面试宝典》上看到这样一道题：

         一个字符串中可能包含a~z中的多个字符，如有重复，如String data="aavzcadfdsfsdhshgWasdfasdf"，求出现次数最多的那个字母及次数，如有多个重复的则都求出。

         看了一下书中的解题思路感觉比较复杂，不容易理解。写法上效率也比较低。这里根据自己的想法试着写了另外一种方法。欢迎大家讨论指导。

package main.java.Chapter_07.Section_1;import java.util.ArrayList;import java.util.Collections;import java.util.Date;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Set;import java.util.TreeSet;public class Example3 {public static void main(String[] args) {//为了测试性能，字符串写的很长。String input ="avzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzc"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh"+ "adfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdhshgWasdfasdfffffdddaaaavzcadfdsfsdh";Long time1 = new Date().getTime();new Example3().doString2(input);Long time2 = new Date().getTime();new Example3().doString(input);Long time3 = new Date().getTime();System.out.println("#################################");System.out.println(time2 - time1);System.out.println(time3 - time2);}/** * 自己的写法 * 思路： * （1）将字符串转换成char数组 * （2）将char放入map中，以char为key，char出现的次数为value。 * （3）用max记录出现最多的次数 * （4）遍历map找出最大次数和出现最多的字符 * @param input */public void doString2(String input){Map<Character,Integer> map = new HashMap<Character,Integer>();char[] chars = input.toCharArray();Integer max = 0;for (char c : chars) {Integer count = map.get(c);count = count ==null?1:++count;map.put(c, count);if(count>max){max = count;}}System.out.println("max "+ max);Set<Character> set = map.keySet();for (Character c : set) {if(max.compareTo(map.get(c))==0){System.out.println("max data "+c);}}}/** * 书中的写法 * @param input */public void doString(String input){char[] chars = input.toCharArray();ArrayList lists = new ArrayList<>();TreeSet set = new TreeSet<>();for (int i = 0; i < chars.length; i++) {lists.add(String.valueOf(chars[i]));set.add(String.valueOf(chars[i]));}//System.out.println(set);Collections.sort(lists);//System.out.println(lists);StringBuffer sb = new StringBuffer();for (int i = 0; i < lists.size(); i++) {sb.append(lists.get(i));}input =sb.toString();//System.out.println(input);int max = 0 ;String maxString = "";ArrayList maxlist = new ArrayList<>();Iterator its =set.iterator();while (its.hasNext()) {String os = (String) its.next();int begin = input.indexOf(os);int end = input.lastIndexOf(os);int value = end -begin +1;if(value > max){max = value;maxString = os;//记录最长的字符串第一次出现的地方，为了下面过滤maxlist.add(os);}else if(value == max){maxlist.add(os);}}//这个地方逻辑有点绕。找出 第一次最长字符串出现的位置，在这之前加入 maxlist中的数据都是假的int index =0;for (int i = 0; i < maxlist.size(); i++) {if(maxlist.get(i).equals(maxString)){index = i;break;}}System.out.println("max data");for (int i = index; i < maxlist.size(); i++) {System.out.println(maxlist.get(i));}System.out.println("max "+max);}}

运行结果：

max 2132max data dmax datadmax 2132#################################632