class Solution {
public:
int f( int * A , int n ) {
for( int i = 0 ; i < n ; i++ ) {
int index = abs(A[i]) - 1;
if( index < n && A[index] > 0 ) {
A[index] *= -1;
}
}
int i = 0;
for( ; i < n ; i++ ) {
if( A[i] > 0 ) {
break;
}
}
return i + 1;
}
int firstMissingPositive(int A[], int n) {
int index = 0;
for( int i = 0 ; i < n ; i++ ) {
if( A[i] <= 0 ) {
int t = A[i];
A[i] = A[index];
A[index] = t;
index++;
}
}
//cout << "Index = " << index << " and a[index] = " << A[index] << endl;
return f(&A[index], n - index);
}
};
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