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amejiarosarioamejiarosario
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fix(bst) pre/post/in-order
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‎src/data-structures/trees/binary-search-tree.js‎

Lines changed: 15 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -65,9 +65,9 @@ class BinarySearchTree {
6565
// search for the parent of the element
6666
while (current) {
6767
if (current.value === value) {
68-
if (parent.value < current.value && parent.left.value === value) {
69-
parent.left = current.left;
70-
}
68+
// if (parent.value < current.value && parent.left.value === value) {
69+
parent.left = current.left;
70+
// }
7171
return true;
7272
}
7373
parent = current;
@@ -121,7 +121,8 @@ class BinarySearchTree {
121121
}
122122

123123
/**
124-
* Breath-first search for a tree (always starting from the root element)
124+
* Breath-first search for a tree (always starting from the root element).
125+
*
125126
*/
126127
* bfs() {
127128
const queue = new Queue();
@@ -137,6 +138,8 @@ class BinarySearchTree {
137138

138139
/**
139140
* Depth-first search for a tree (always starting from the root element)
141+
*
142+
* @see preOrderTraversal Similar results to the pre-order transversal.
140143
*/
141144
* dfs() {
142145
const stack = new Stack();
@@ -146,7 +149,8 @@ class BinarySearchTree {
146149
while (!stack.isEmpty()) {
147150
const node = stack.remove();
148151
yield node;
149-
node.descendents.forEach(child => stack.add(child));
152+
// reverse array, so left gets removed before right
153+
node.descendents.reverse().forEach(child => stack.add(child));
150154
}
151155
}
152156

@@ -164,14 +168,15 @@ class BinarySearchTree {
164168
}
165169

166170
/**
167-
* Pre-order traversal on a tree
171+
* Pre-order traversal on a tree. Similar results to DFS
168172
*
169173
* @param {TreeNode} node first node to start the traversal
174+
* @see dfs similar results to the breath first search
170175
*/
171176
* preOrderTraversal(node = this.root) {
172177
yield node;
173-
if (node.left) { yield* this.inOrderTraversal(node.left); }
174-
if (node.right) { yield* this.inOrderTraversal(node.right); }
178+
if (node.left) { yield* this.preOrderTraversal(node.left); }
179+
if (node.right) { yield* this.preOrderTraversal(node.right); }
175180
}
176181

177182
/**
@@ -180,8 +185,8 @@ class BinarySearchTree {
180185
* @param {TreeNode} node first node to start the traversal
181186
*/
182187
* postOrderTraversal(node = this.root) {
183-
if (node.left) { yield* this.inOrderTraversal(node.left); }
184-
if (node.right) { yield* this.inOrderTraversal(node.right); }
188+
if (node.left) { yield* this.postOrderTraversal(node.left); }
189+
if (node.right) { yield* this.postOrderTraversal(node.right); }
185190
yield node;
186191
}
187192
}

‎src/data-structures/trees/binary-search-tree.spec.js‎

Lines changed: 31 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -2,6 +2,7 @@ const BinarySearchTree = require('./binary-search-tree');
22

33
describe('Binary Search Tree', () => {
44
let bst;
5+
const getValues = treeGenerator => Array.from(treeGenerator).map(node => node.value);
56

67
beforeEach(() => {
78
bst = new BinarySearchTree();
@@ -41,20 +42,29 @@ describe('Binary Search Tree', () => {
4142
});
4243

4344
describe('when has items', () => {
44-
let n2;
45+
let n5;
4546
let root;
4647

4748
beforeEach(() => {
49+
// 10
50+
// / \
51+
// 5 30
52+
// / / \
53+
// 4 15 40
54+
// /
55+
// 3
4856
root = bst.add(10);
49-
n2 = bst.add(2);
57+
n5 = bst.add(5);
5058
bst.add(30);
5159
bst.add(40);
5260
bst.add(15);
61+
bst.add(4);
62+
bst.add(3);
5363
});
5464

5565
describe('#find', () => {
5666
it('should find the value 2', () => {
57-
expect(bst.find(2)).toBe(n2);
67+
expect(bst.find(5)).toBe(n5);
5868
});
5969

6070
it('should NOT find the value 20', () => {
@@ -64,12 +74,14 @@ describe('Binary Search Tree', () => {
6474

6575
xdescribe('#remove', () => {
6676
it('should remove value 2', () => {
77+
expect(bst.toArray()).toEqual([10, 2, 30, undefined, undefined, 15, 40, undefined, undefined, undefined, undefined]);
78+
expect(Array.from(bst.preOrderTraversal()).map(n => n.value)).toEqual([10, 2, 30, 15, 40]);
6779
expect(bst.remove(2)).toBe(true);
68-
expect(bst.toArray()).toEqual([10, undefined, 30, undefined, undefined, 15, 40]);
80+
expect(Array.from(bst.preOrderTraversal()).map(n => n.value)).toEqual([10, 30, 15, 40]);
6981
expect(root.left).toBe(undefined);
7082
});
7183

72-
it('should return false for removing unexisting value 20', () => {
84+
xit('should return false for removing unexisting value 20', () => {
7385
expect(bst.remove(20)).toBe(false);
7486
});
7587
});
@@ -78,83 +90,66 @@ describe('Binary Search Tree', () => {
7890
it('should visit nodes on BFS order using iterator', () => {
7991
const bfs = bst.bfs();
8092
expect(bfs.next().value).toBe(root); // 10
81-
expect(bfs.next().value).toBe(n2);
93+
expect(bfs.next().value).toBe(n5);
8294
expect(bfs.next().value.value).toBe(30);
95+
expect(bfs.next().value.value).toBe(4);
8396
expect(bfs.next().value.value).toBe(15);
8497
expect(bfs.next()).toMatchObject({ value: { value: 40 }, done: false });
98+
expect(bfs.next()).toMatchObject({ value: { value: 3 }, done: false });
8599
expect(bfs.next().done).toBe(true);
86100
});
87101

88102
it('should generate an array from bfs', () => {
89-
const nodes = Array.from(bst.bfs());
90-
const values = nodes.map(node => node.value);
91-
expect(values).toEqual([10, 2, 30, 15, 40]);
103+
expect(getValues(bst.bfs())).toEqual([10, 5, 30, 4, 15, 40, 3]);
92104
});
93105
});
94106

95107
describe('#dfs', () => {
96108
it('should visit nodes on dfs order using iterator', () => {
97109
const dfs = bst.dfs();
98110
expect(dfs.next().value).toBe(root); // 10
111+
expect(dfs.next().value).toBe(n5);
112+
expect(dfs.next().value.value).toBe(4);
113+
expect(dfs.next().value.value).toBe(3);
99114
expect(dfs.next().value.value).toBe(30);
100-
expect(dfs.next()).toMatchObject({ value: { value: 40 }, done: false });
101115
expect(dfs.next().value.value).toBe(15);
102-
expect(dfs.next().value).toBe(n2);
116+
expect(dfs.next()).toMatchObject({ value: { value: 40 }, done: false });
103117
expect(dfs.next().done).toBe(true);
104118
});
105119

106120
it('should generate an array from dfs', () => {
107121
const nodes = Array.from(bst.dfs());
108122
const values = nodes.map(node => node.value);
109-
expect(values).toEqual([10, 30, 40, 15, 2]);
123+
expect(values).toEqual([10, 5, 4, 3, 30, 15, 40]);
110124
});
111125
});
112126

113127
describe('#inOrderTraversal', () => {
114-
it('should visit nodes on order using iterator', () => {
115-
const ordered = bst.inOrderTraversal();
116-
117-
expect(ordered.next().value).toBe(n2);
118-
expect(ordered.next().value).toBe(root); // 10
119-
expect(ordered.next().value.value).toBe(15);
120-
expect(ordered.next().value.value).toBe(30);
121-
expect(ordered.next()).toMatchObject({ value: { value: 40 }, done: false });
122-
expect(ordered.next().done).toBe(true);
123-
});
124-
125128
it('should generate an array', () => {
126-
const nodes = Array.from(bst.inOrderTraversal());
127-
const values = nodes.map(node => node.value);
128-
expect(values).toEqual([2, 10, 15, 30, 40]);
129+
expect(getValues(bst.inOrderTraversal())).toEqual([3, 4, 5, 10, 15, 30, 40]);
129130
});
130131
});
131132

132133
describe('#preOrderTraversal', () => {
133134
it('should generate an array from preOrderTraversal', () => {
134135
const nodes = Array.from(bst.preOrderTraversal());
135136
const values = nodes.map(node => node.value);
136-
expect(values).toEqual([10, 2, 15, 30, 40]);
137+
expect(values).toEqual([10, 5, 4, 3, 30, 15, 40]);
137138
});
138139
});
139140

140141
describe('#postOrderTraversal', () => {
141142
it('should generate an array from postOrderTraversal', () => {
142143
const nodes = Array.from(bst.postOrderTraversal());
143144
const values = nodes.map(node => node.value);
144-
expect(values).toEqual([2, 15, 30, 40, 10]);
145+
expect(values).toEqual([3, 4, 5, 15, 40, 30, 10]);
145146
});
146147
});
147148

148149
describe('#toArray', () => {
149150
it('should serialize the tree as an array', () => {
150-
expect(bst.toArray()).toEqual([10, 2, 30, undefined, undefined, 15, 40,
151-
undefined, undefined, undefined, undefined]);
152-
});
153-
154-
it('should serialize new tree', () => {
155-
bst.add(3);
156-
expect(bst.toArray()).toEqual([10, 2, 30, undefined, 3, 15, 40,
157-
undefined, undefined, undefined, undefined, undefined, undefined]);
151+
expect(bst.toArray()).toEqual([10, 5, 30, 4, undefined, 15, 40, 3,
152+
undefined, undefined, undefined, undefined, undefined, undefined, undefined]);
158153
});
159154
});
160155
});

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