bool first_goes_to_left_of(int first, int second) {
    if (first %2 == 0) { //if first is even
        if (second %2 == 0) //and second is even
            return first < second; //sort by increasing order
        else  //and second is odd
            return true; //first goes to left
    } else { //if first is odd
        if (second %2 == 0) //and second is even
            return false; //second goes to left
        else  //and second is odd
            return second < first; //sort by decreasing order
    }
}
 
#include <algorithm>
#include <iostream>
#include <iterator>
 
int main() {
    int a[10]={4,6,9,1,2,3,7,5,8,0};
    std::sort(a, a+10, first_goes_to_left_of);
    std::copy(a, a+10, std::ostream_iterator<int>(std::cout, " "));
}

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