遇到一個問題，網上有很多教程，在沒看的情況下，自己先寫了幾種方法，僅供參考：

Python實現方式：（三種方法，執行效率有差異）

# _*_ coding:utf-8 _*_
import time

# 傳參方式
str = "=WUKVJPLKKPYBUI=JAOCFCJJIYKGNAVZPEKOLIQNEBVGILOLYOJZJUJJNEHOSJGDXQRUYGZIKCNGKKBBGLPLVHXETIZQBNTXMGTTAVRNSNRCNVZVWKFQHOSMKACKYTUQLUMALTRAFLGKYRTHKSGDOUVYWYOJITYPVPIYQIRPNWTJFYKMIGZZZYXCYIVLFXSJNE+"


# str = "abcdefgadbc"
# str = input("Please input a number:")

# 方法一
def m1(str):
    list1 = []
    list2 = []
    for i in range(len(str)):
        if str[i] not in list1 and str[i] not in list2:
            list1.append(str[i])
        else:
            if str[i] in list1:
                list2.append(str[i])
                list1.remove(str[i])
            else:
                list2.append(str[i])
    print("%s\t%d" % (list1[0], str.index(list1[0])))


# 方法二
def m2(str):
    m = 0
    list = []
    for i in range(len(str)):
        for j in range(i + 1, len(str)):
            if str[i] == str[j]:
                m += 1
                list.append(str[i])
        if m == 0 and str[i] not in list:
            print(str[i], i)
            break
        else:
            m = 0
        # print(str[i])


# 方法三
def m3(str):
    bo = []
    for i in range(len(str)):
        bo.append(False)
    for i in range(len(str)):
        if bo[i] == False:
            for j in range(i + 1, len(str)):
                if bo[j] == False:
                    if str[i] == str[j]:
                        bo[i] = True
                        bo[j] = True
    for k in range(len(bo)):
        if bo[k] == False:
            print("%s\t%d" % (str[k], k))
            break


# 統計執行時間
start = time.clock()
m1(str)
end = time.clock()
print("Running time: %s Seconds" % (end - start))

# 方法一用時：Running time: 0.00020000000000000573 Seconds
# 方法二用時：Running time: 0.0019740000000000035 Seconds
# 方法三用時：Running time: 0.0005379999999999968 Seconds



 

Java實現方式：

public class TEST_java {
	public static void main(String[] args) {
		// System.out.println("請輸入字串:");
		// Scanner sc = new Scanner(System.in);
		// String str = sc.nextLine();
		String str = "abcdefabcdef+";
		boolean[] boa = new boolean[str.length()];
		int i, j, k = 0;
		char test, cha;
		for (i = 0; i < str.length(); i++) {
			if (boa[i] == false) {
				test = str.charAt(i);
				for (j = i + 1; j < str.length(); j++) {
					if (boa[j] == false) {
						cha = str.charAt(j);
						if (cha == test) {
							boa[i] = true;
							boa[j] = true;
						}
					}
				}
			}
		}
		for (k = 0; k < boa.length; k++) {
			if (boa[k] == false) {
				System.out.println(str.charAt(k) + "\t" + k);
				break;
			}
		}
	}
}
 

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