取出一个字符串中字母出现的次数。如：字符串："abcde%^kka27qoq" ，输出格式为： a(2)b(1)k(2)...

来源：互联网发布：蛙5火箭知乎编辑：程序博客网时间：2024/06/06 02:05

考虑到效率问题，鄙人发现网上应该有两种不同的方法，经过验证发现，用for循环实现比较快捷(花的时间少)：

程序如下：

（1）for循环简单思路就是把源字符串转换成字符数组并挨个比较；

（2）另外一种方法是用Map集合，由于Map集合中是不允许有键重复，利用这一特点实现；

import java.util.HashMap;import java.util.Map;import java.util.Map.Entry;import java.util.Set;public class 计算字符个数效率 {<span style="white-space:pre"></span>public static void main(String[] args) {<span style="white-space:pre"></span>String string = "abcde%^kka27qoq";<span style="white-space:pre"></span>System.out.println(string);<span style="white-space:pre"></span>long start = System.nanoTime();<span style="white-space:pre"></span>fun1(string);<span style="white-space:pre"></span>long end = System.nanoTime();<span style="white-space:pre"></span>System.out.println("\ncost time:" + (end - start));<span style="white-space:pre"></span>start = System.nanoTime();<span style="white-space:pre"></span>fun2(string);<span style="white-space:pre"></span>end = System.nanoTime();<span style="white-space:pre"></span>System.out.println("\ncost time:" + (end - start));<span style="white-space:pre"></span>}<span style="white-space:pre"></span>public static void fun1(String str) {<span style="white-space:pre"></span>char[] cs = str.toCharArray();<span style="white-space:pre"></span>for (int i = 0; i < cs.length; i++) {<span style="white-space:pre"></span>if (cs[i] == ' ') {<span style="white-space:pre"></span>continue;<span style="white-space:pre"></span>}<span style="white-space:pre"></span>int count = 1;<span style="white-space:pre"></span>for (int j = i + 1; j < cs.length; j++) {<span style="white-space:pre"></span>if (cs[i] == cs[j]) {<span style="white-space:pre"></span>count++;<span style="white-space:pre"></span>cs[j] = ' ';<span style="white-space:pre"></span>}<span style="white-space:pre"></span>}<span style="white-space:pre"></span>System.out.print(cs[i] + "(" + count + ")");<span style="white-space:pre"></span>}<span style="white-space:pre"></span>}<span style="white-space:pre"></span>public static void fun2(String str) {<span style="white-space:pre"></span>Map<Character, Integer> map = new HashMap<Character, Integer>();<span style="white-space:pre"></span>char[] cs = str.toCharArray();<span style="white-space:pre"></span>for (int i = 0; i < cs.length; i++) {<span style="white-space:pre"></span>Integer count = map.get(cs[i]);<span style="white-space:pre"></span>if (count == null) {<span style="white-space:pre"></span>count = 0;<span style="white-space:pre"></span>}<span style="white-space:pre"></span>map.put(cs[i], count + 1);<span style="white-space:pre"></span>}<span style="white-space:pre"></span>Set<Entry<Character, Integer>> entrySet = map.entrySet();<span style="white-space:pre"></span>for (Entry<Character, Integer> entry : entrySet) {<span style="white-space:pre"></span>System.out.print(entry.getKey() + "(" + entry.getValue() + ")");<span style="white-space:pre"></span>}<span style="white-space:pre"></span>}}

结果如下：

0 0