Is it possible to optimize so that the res array is on the stack rather than on the heap? What needs to be done for this?

In Go, arrays declared locally within a function are usually allocated on the stack if the compiler can guarantee that they do not escape the scope of the function. To ensure the array res is on the stack:

• Declare the array with a fixed size locally, for example var res [N]int.
• Avoid passing pointers to this array outside the function (to prevent escape analysis).

If the compiler determines that the array "escapes" (escape analysis), it will allocate it on the heap. Therefore, it's important that the array is not returned from the function or stored in global variables.

Example:

func example() {
    var res [100]int // array on the stack
    // work with res
}

However, if you use slices with a dynamic size, the underlying array is usually allocated on the heap.