An unsorted array[1…n], range is from 1…N+1，a number is missing, find it. performance。

An unsorted array[1…n], range is from 1…N+1，a number is missing, find it. performance。

Unsorted array use xor besides sum up method and bit vector in msb method. O(n)

int F(int* a, int N)
{
int s=0;
for(int i=1;i<=N;i++)
{
s=s xor i xor a[i];
}
return s xor n+1;
}