题解 | 找出字符串中第一个只出现一次的字符

using System;
public class Program {
    public static void Main() {
        string line;
        while ((line = System.Console.ReadLine ()) !=
                null) { // 注意 while 处理多个 case
            char[] S = line.ToCharArray();
            char OC = ' ';
            for (int i = 0; i < line.Length; i++) {
                if (!line.Remove(i, 1).Contains(S[i].ToString())) {
                    OC = S[i];
                    break;
                }
            }
            if (OC == ' ') {
                Console.WriteLine(-1);
            } else {
                Console.WriteLine(OC);
            }
        }
    }
}