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);
}
}