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Commit 8e8b623

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bst
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‎book/chapters/tree--self-balancing-bst.adoc‎

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@@ -52,11 +52,84 @@ include::{codedir}/data-structures/trees/tree-rotations.js[tag=rightRotation]
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- `grandparent` this the current's node parent. E.g. `node 4`.
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The `swapParentChild` as it name says, swap the children.
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For our example, it swaps `node 4`'s left children from `node 3` to `node 2`.
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Take a look at the implementation
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.Swap Parent and Child Implementation
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[source, javascript]
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----
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include::{codedir}/data-structures/trees/tree-rotations.js[tag=swapParentChild]
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----
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After `swapParentChild`, we have the following:
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----
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4
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/
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2 - 3*
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/
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1
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----
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Still not quite what we want.
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So, `newParent.setRightAndUpdateParent(node)` will make `node 3` the right child of `node 2`.
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Finally, we remove left child of `node 3` to be `null`.
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----
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4
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/
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2
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/ \
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1 3*
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----
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Check out the <<Single Right Rotation, rightRotation>> implementation again. It should make more sense to you now.
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This rotation is also known as `RR rotation`.
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=== Single Left Rotation
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Left rotation is similar to the `rightRotation` we explained above.
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.Single left rotation implementation
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[source, javascript]
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----
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include::{codedir}/data-structures/trees/tree-rotations.js[tag=leftRotation]
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----
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As you can see, this function is just the opposite of `rightRotation`. Where ever we used the right now we use the left here and vice versa.
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This rotation is also known as `LL rotation`.
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If you are curious about the `setRightAndUpdateParent`. Here's the implementation:
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.Set and update parent implementation
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[source, javascript]
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----
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include::{codedir}/data-structures/trees/binary-tree-node.js[tag=setAndUpdateParent]
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----
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=== Left Right Rotation
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This time are we going to do a double rotation.
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.Left-Right rotation implementation
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[source, javascript]
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----
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include::{codedir}/data-structures/trees/tree-rotations.js[tag=leftRightRotation]
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----
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As you can see we do a left and then a right rotation. This is also called `LR rotation`
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=== Right Left Rotation
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Very similar to `leftRightRotation`. The difference is that we rotate right and then left.
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.Right-Left rotation implementation
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[source, javascript]
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----
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include::{codedir}/data-structures/trees/tree-rotations.js[tag=rightLeftRotation]
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----
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This rotation is also refered as `RL rotation`.

‎src/data-structures/trees/binary-tree-node.js‎

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@@ -17,6 +17,7 @@ class BinaryTreeNode {
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this.parentSide = null;
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}
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// tag::setAndUpdateParent[]
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/**
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* Set a left node descendents.
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* Also, children get associated to parent.
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node.parentSide = RIGHT;
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}
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}
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// end::setAndUpdateParent[]
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/**
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* Tell if is parent's left or right child

‎src/data-structures/trees/tree-rotations.js‎

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@@ -50,7 +50,6 @@ function leftRotation(node) {
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const newParent = node.right;
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const grandparent = node.parent;
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swapParentChild(node, newParent, grandparent);
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// do LL rotation
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const newParent = node.left; // E.g., node 2
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const grandparent = node.parent; // E.g., node 4
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// swap node 4 left children (node 3) with node 2.
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swapParentChild(node, newParent, grandparent);
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// do RR rotation
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// update right child on node 2 to be node 3,
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// also make node 2 the new parent of node 3.
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newParent.setRightAndUpdateParent(node);
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// remove node 3 left child (so it doesn't point to node 2)
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node.setLeftAndUpdateParent(null);
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return newParent;

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