在特定规律的数组中查找某元素

给定数组A[n]，其中 A[i+1] = A[i]+1 OR A[i]-1,和数字k，请用最有效的方式在数组A中查找k。

Given an array A[n] such that A[i+1] = A[i]+1 OR A[i]-1, and a number k, can you determine in most efficient way whether k is present in A[n] or not?

对A[0],如果它不等于k，求出他和k相差的绝对值diff，考查0+diff处的值。如果不等于k，重复以上步骤。直到找到k，或者遍历完数组。

bool Find_elem(int a[],int length,int expectedNum)
{
	int i = 0;
	while (i < length)
	{
		if (a[i] == expectedNum)
		{
			return true;
		}
		else
		{
			int diff = abs(expectedNum - a[i]);
			i = i+diff;
		}
	}
	return false;
}