According to AVL tree wiki
The balance factor is calculated as follows: balanceFactor = height(left-subtree) - height(right-subtree). For each node checked, if the balance factor remains −1, 0, or +1 then no rotations are necessary.
However, in OCaml, it seems it uses balance factor of 2
let bal l x d r =
let hl = match l with Empty -> 0 | Node(_,_,_,_,h) -> h in
let hr = match r with Empty -> 0 | Node(_,_,_,_,h) -> h in
if hl > hr + 2 then begin
match l with
Empty -> invalid_arg "Map.bal"
| Node(ll, lv, ld, lr, _) ->
if height ll >= height lr then
create ll lv ld (create lr x d r)
else begin
match lr with
Empty -> invalid_arg "Map.bal"
| Node(lrl, lrv, lrd, lrr, _)->
create (create ll lv ld lrl) lrv lrd (create lrr x d r)
end
end else if hr > hl + 2 then begin
match r with
Empty -> invalid_arg "Map.bal"
| Node(rl, rv, rd, rr, _) ->
if height rr >= height rl then
create (create l x d rl) rv rd rr
else begin
match rl with
Empty -> invalid_arg "Map.bal"
| Node(rll, rlv, rld, rlr, _) ->
create (create l x d rll) rlv rld (create rlr rv rd rr)
end
end else
Node(l, x, d, r, (if hl >= hr then hl + 1 else hr + 1))
Why?
