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Commit 1fa9341

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fix(tree-rotations): prevent losing nodes
LL Rotation, lose the newParent previous right node; RR Rotation too Fixes: amejiarosario#30 
1 parent 3356e1f commit 1fa9341

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3 files changed

+125
-22
lines changed

3 files changed

+125
-22
lines changed

‎src/data-structures/trees/avl-tree.spec.js‎

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -144,4 +144,23 @@ describe('AvlTree', () => {
144144
expect(tree.root).toBe(n);
145145
});
146146
});
147+
148+
describe('balance without loosing nodes', () => {
149+
beforeEach(() => {
150+
tree.add(16);
151+
tree.add(4);
152+
tree.add(32);
153+
tree.add(8);
154+
tree.add(2);
155+
});
156+
157+
it('should have all nodes', () => {
158+
expect(tree.toArray()).toEqual([16, 4, 32, 2, 8, null, null, null, null, null, null]);
159+
});
160+
161+
it('should rebalance and keep all nodes', () => {
162+
tree.add(1);
163+
expect(tree.toArray()).toEqual([4, 2, 16, 1, null, 8, 32, null, null, null, null, null, null]);
164+
});
165+
});
147166
});

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

Lines changed: 44 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,6 @@
22
/**
33
* Swap parent's child
44
*
5-
*
65
* @example Child on the left side (it also work for the right side)
76
*
87
* p = parent
@@ -34,7 +33,7 @@ function swapParentChild(oldChild, newChild, parent) {
3433
/**
3534
* Single Left Rotation (LL Rotation)
3635
*
37-
* @example: tree with values 1-2-3-4
36+
* @example: #1 tree with values 1-2-3-4
3837
*
3938
* 1 1
4039
* \ \
@@ -43,21 +42,34 @@ function swapParentChild(oldChild, newChild, parent) {
4342
* 3 2* 4
4443
* \
4544
* 4
46-
* @param {TreeNode} node
47-
* @returns {TreeNode} new parent after the rotation
45+
*
46+
* @example: #2 left rotation
47+
*
48+
* 1 1
49+
* \ \
50+
* 4* 16
51+
* / \ / \
52+
* 2 16 -- left-rotation(4) -> 4 32
53+
* / \ / \ \
54+
* 8 32 2 8 64
55+
* \
56+
* 64
57+
* @param {TreeNode} node current node to rotate (e.g. 4)
58+
* @returns {TreeNode} new parent after the rotation (e.g. 16)
4859
*/
4960
function leftRotation(node) {
50-
const newParent = node.right; // E.g., node 3
61+
const newParent = node.right; // E.g., node 16
5162
const grandparent = node.parent; // E.g., node 1
63+
const previousLeft = newParent.left; // E.g., node 8
5264

53-
// swap node 1 left child from 2 to 3.
65+
// swap parent of node 4 from node 1 to node 16
5466
swapParentChild(node, newParent, grandparent);
5567

56-
// Update node 3 left child to be 2, and
57-
// updates node 2 parent to be node 3 (instead of 1).
68+
// Update node 16 left child to be 4, and
69+
// updates node 4 parent to be node 16 (instead of 1).
5870
newParent.setLeftAndUpdateParent(node);
59-
// remove node 2 left child (previouly was node 3)
60-
node.setRightAndUpdateParent(null);
71+
// set node4 right child to be previousLeft (node 8)
72+
node.setRightAndUpdateParent(previousLeft);
6173

6274
return newParent;
6375
}
@@ -66,8 +78,7 @@ function leftRotation(node) {
6678
// tag::rightRotation[]
6779
/**
6880
* Single Right Rotation (RR Rotation)
69-
*
70-
* @example rotate node 3 to the right
81+
* @example: #1 rotate node 3 to the right
7182
*
7283
* 4 4
7384
* / /
@@ -77,22 +88,34 @@ function leftRotation(node) {
7788
* /
7889
* 1
7990
*
91+
* @example: #2 rotate 16 to the right and preserve nodes
92+
* 64 64
93+
* / /
94+
* 16* 4
95+
* / \ / \
96+
* 4 32 -- right-rotation(16) --> 2 16
97+
* / \ / / \
98+
* 2 8 1 8 32
99+
* /
100+
* 1
101+
*
80102
* @param {TreeNode} node
81-
* this is the node we want to rotate to the right. (E.g., node 3)
82-
* @returns {TreeNode} new parent after the rotation (E.g., node 2)
103+
* this is the node we want to rotate to the right. (E.g., node 16)
104+
* @returns {TreeNode} new parent after the rotation (E.g., node 4)
83105
*/
84106
function rightRotation(node) {
85-
const newParent = node.left; // E.g., node 2
86-
const grandparent = node.parent; // E.g., node 4
107+
const newParent = node.left; // E.g., node 4
108+
const grandparent = node.parent; // E.g., node 64
109+
const previousRight = newParent.right; // E.g., node 8
87110

88-
// swap node 4 left children (node 3) with node 2.
111+
// swap node 64's left children (node 16) with node 4 (newParent).
89112
swapParentChild(node, newParent, grandparent);
90113

91-
// update right child on node 2 to be node 3,
92-
// also make node 2 the new parent of node 3.
114+
// update node 4's right child to be node 16,
115+
// also make node 4 the new parent of node 16.
93116
newParent.setRightAndUpdateParent(node);
94-
// remove node 3 left child (so it doesn't point to node 2)
95-
node.setLeftAndUpdateParent(null);
117+
// Update 16's left child to be the `previousRight` node.
118+
node.setLeftAndUpdateParent(previousRight);
96119

97120
return newParent;
98121
}

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

Lines changed: 62 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -96,6 +96,39 @@ describe('Tree rotations', () => {
9696
value: 3, left: 2, right: null, parent: 4,
9797
});
9898
});
99+
100+
it('should not lose nodes on LL', () => {
101+
// 1 1
102+
// \ \
103+
// 4* 16
104+
// / \ / \
105+
// 2 16 -- left-rotation(4) -> 4 32
106+
// / \ / \ \
107+
// 8 32 2 8 64
108+
// \
109+
// 64
110+
const n8 = new BinaryTreeNode(8);
111+
const n16 = new BinaryTreeNode(16);
112+
const n32 = new BinaryTreeNode(32);
113+
const n64 = new BinaryTreeNode(64);
114+
115+
n1.setRightAndUpdateParent(n4);
116+
n4.setLeftAndUpdateParent(n2);
117+
n4.setRightAndUpdateParent(n16);
118+
n16.setLeftAndUpdateParent(n8);
119+
n16.setRightAndUpdateParent(n32);
120+
n32.setLeftAndUpdateParent(n64);
121+
122+
const newParent = leftRotation(n4);
123+
124+
expect(newParent).toBe(n16);
125+
expect(n8.toValues()).toMatchObject({
126+
value: 8, left: null, right: null, parent: 4,
127+
});
128+
expect(n4.toValues()).toMatchObject({
129+
value: 4, left: 2, right: 8, parent: 16,
130+
});
131+
});
99132
});
100133

101134
describe('#rightRotation (RR Rotation)', () => {
@@ -145,7 +178,7 @@ describe('Tree rotations', () => {
145178
});
146179
});
147180

148-
it('should last two', () => {
181+
it('should RR last two', () => {
149182
// 1
150183
// \
151184
// 3*
@@ -167,6 +200,34 @@ describe('Tree rotations', () => {
167200
value: 3, left: null, right: null, parent: 2,
168201
});
169202
});
203+
204+
it('should not lose nodes on RR', () => {
205+
// 16* 4
206+
// / \ / \
207+
// 4 32 -- right-rotation(16) --> 2 16
208+
// / \ / / \
209+
// 2 8 1 8 32
210+
// /
211+
// 1
212+
const n8 = new BinaryTreeNode(8);
213+
const n16 = new BinaryTreeNode(16);
214+
const n32 = new BinaryTreeNode(32);
215+
n16.setLeftAndUpdateParent(n4);
216+
n16.setRightAndUpdateParent(n32);
217+
n4.setLeftAndUpdateParent(n2);
218+
n4.setRightAndUpdateParent(n8);
219+
n2.setLeftAndUpdateParent(n1);
220+
221+
const newParent = rightRotation(n16);
222+
223+
expect(newParent).toBe(n4);
224+
expect(n8.toValues()).toMatchObject({
225+
value: 8, left: null, right: null, parent: 16,
226+
});
227+
expect(n16.toValues()).toMatchObject({
228+
value: 16, left: 8, right: 32, parent: 4,
229+
});
230+
});
170231
});
171232

172233
describe('#leftRightRotation (LR Rotation)', () => {

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