题目：在一个字符串中找到第一个只出现一次的字符。如输入abaccdeff，则输出b。

代码如下：

import java.util.Scanner;

public class Test2 {

public static char first(String s)

{

char result = '0';

char t;

int num[] = new int[50];

for (int i = 0; i < s.length(); i ++)

{

t = s.charAt(i);

if ( t >= 'a' && t <= 'z' )

{

num[t - 'a']++;

}

else if (t >= 'A' && t <= 'Z')

{

num[t - 'A' + 26] ++;

}

}

for (int i = 0; i < num.length; i ++)

{

if (num[i] == 1)

{

if (i >= 0 && i <=26)

{

result = (char)(i + 'a');

}

else

result = (char)(i - 26 + 'A');

break;

}

}

return result;

}

public static void main(String[] args) {

System.out.println("请输入字符串:");

Scanner reader = new Scanner(System.in);

String s = reader.next();

char c = first(s);

System.out.println(c);

}

}