Solution.java

class Solution {
    public int[] findErrorNums(int[] nums) {
        int res = 0;
        for (int num : nums) {
            res ^= num;
        }
        for (int i = 1, n = nums.length; i < n + 1; ++i) {
            res ^= i;
        }
        int pos = 0;
        while ((res & 1) == 0) {
            res >>= 1;
            ++pos;
        }
        int a = 0, b = 0;
        for (int num : nums) {
            if (((num >> pos) & 1) == 0) {
                a ^= num;
            } else {
                b ^= num;
            }
        }
        for (int i = 1, n = nums.length; i < n + 1; ++i) {
            if (((i >> pos) & 1) == 0) {
                a ^= i;
            } else {
                b ^= i;
            }
        }
        for (int num : nums) {
            if (num == a) {
                return new int[]{a, b};
            }
        }
        return new int[]{b, a};
    }
}