According to GPT

```go
for len(stack) > 0 {
    pop := stack[len(stack)-1] // Pop the top element from the stack.
    stack = stack[:len(stack)-1] // Remove the popped element from the stack.
    sb += fmt.Sprintf("%d", pop) // Append the popped binary digit to the result string.
}

**Time Complexity:**

- **Stack Operations:** Popping from a slice is O(1).
- **String Concatenation:** Each `sb += fmt.Sprintf("%d", pop)` operation involves concatenating a string to `sb`. Concatenating strings in Go with `+=` within a loop has O(k) complexity where `k` is the length of the string being concatenated, leading to O(log₂(num)²) due to repeated reallocation and copying of the string.