First Missing Positive

class Solution {
public:
int firstMissingPositive(int A[], int n) {
for(size_t i=0;i!=n;)
{
if(A[i]!=(i+1) && A[i]>=1 &&A[i]<=n &&A[A[i]-1]!=A[i] )
{
int tmp=A[A[i]-1];
A[A[i]-1]=A[i];
A[i]=tmp;
}
else
{
i++;
}
}
for(size_t i=0;i!=n;i++)
{
if(A[i]!=i+1)
{
return i+1;
}
}
return n+1;
}
};