题目：一个整型数组里除了两个数字之外，其他的数字都出现了两次。请写程序找出这两个只出现一次的数字。要求时间复杂度是O(n)，空间复杂度是O(1)。
// Find two numbers which only appear once in an array
// Input: data - an array contains two number appearing exactly once,
// while others appearing exactly twice
// Output: num1 - the first number appearing once in data
// num2 - the second number appearing once in data
staticvoid FindNumsAppearOnce(int[] arr, outint num1, outint num2)
{
num1 = num2 = 0;
if (arr.Length < 2)
{
return;
}
// get num1 ^ num2
int resultExclusiveOR = 0;
for (int i = 0; i < arr.Length; ++i)
{
resultExclusiveOR ^= arr[i];
}
// get index of the first bit, which is 1 in resultExclusiveOR
int indexOf1 = FindFirstBitIs1(resultExclusiveOR);
for (int j = 0; j < arr.Length; ++j)
{
// divide the numbers in data into two groups,
// the indexOf1 bit of numbers in the first group is 1,
// while in the second group is 0
if (IsBit1(arr[j], indexOf1) ==1)
num1 ^= arr[j];
else
num2 ^= arr[j];
}
}
// Find the index of first bit which is 1 in num (assuming not 0)
staticint FindFirstBitIs1(int num)
{
int indexBit = 0;
while (((num & 1) == 0) && (indexBit < 32))
{
num = num >> 1;
++indexBit;
}
return indexBit;
}
// Is the indexBit bit of num 1?
staticint IsBit1(int num, int indexBit)
{
num = num >> indexBit;
return num & 1;
}