Interchange with leader??

[p-nut buddha]

Can someone translate "Interchange with leader" to English for me? The
method commentary says:

// search forward for leader

// swap

Ok, "search forward", does that just mean to search forward in the array?
Doing so wouldn't seem to guarantee that you would swap with a leaf.

[p-nut buddha]

Once I understood the block equivalence class it became clear what to do.

Post by p-nut buddha
Can someone translate "Interchange with leader" to English for me? The
// search forward for leader
// swap
Ok, "search forward", does that just mean to search forward in the array?
Doing so wouldn't seem to guarantee that you would swap with a leaf.