Changing from recursion to iteration
void func(int a, int b, int c, int d) {
    //something
    //non-recursive
    //here..

    for (i=0; i<data.length; i++) {
        if (!data[i].x) {
            data[i].x = 1;
            if (a == data[i].value1)
                func(data[i].value2,b,c,d);
            else if (a == data[i].value2)
                func(data[i].value1,b,c,d);

            data[i].x = 0;
        }
    }
}