原题链接: https://oj.leetcode.com/problems/single-number/

PS: 利用异或运算可以用来加解密.

public int singleNumber(int[] A) {
    int num = 0;

    for (int i = 0, length = A.length; i < length; i++) {
        num ^= A[i];
    }

    return num;
}