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Challenge 2

Insert items into a BST and search.

Challenge 2: BST

In this challenge you will insert items into a BST and search. The tree is represented with lists.

Values: [5, 3, 7, 2, 4]. Search: 4. Output: True.

BST gives ordered search with left-smaller, right-larger rule; average O(log n).

Practice BST insert and search

Write bst_search(tree, val). Check if val exists in the tree. Print True with print(bst_search(build_bst([5, 3, 7, 2, 4]), 4)).

Starter code

solution.py
def bst_search(tree, val):
    # BST search

Sample solution

solution.py
def bst_search(tree, val):
    # BST search
    if tree is None:
        return False
    if tree[0] == val:
        return True
    if val < tree[0]:
        return bst_search(tree[1], val)
    return bst_search(tree[2], val)
def bst_insert(tree, val):
    if tree is None:
        return [val, None, None]
    if val < tree[0]:
        tree[1] = bst_insert(tree[1], val)
    else:
        tree[2] = bst_insert(tree[2], val)
    return tree
def build_bst(values):
    root = None
    for v in values:
        root = bst_insert(root, v)
    return root
print(bst_search(build_bst([5, 3, 7, 2, 4]), 4))

Expected output

True

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Tree node

Question 
[val, ____, right]
Answer 
[val, left, right]

Explanation: left is right.

2 Challenge 2: match the terms

Term Meaning
BST Ordered tree
left Smaller
right Larger
search Search

All lessons in Intermediate

1 Merge sort

  1. Divide and conquer
  2. Merge operation
  3. Full merge sort
  4. Summary - Merge sort

2 Quick sort

  1. Pivot selection
  2. Partitioning
  3. Recursive quick sort
  4. Summary - Quick sort

3 Heap sort

  1. What is a heap?
  2. Heapify
  3. Build heap and sort
  4. Summary - Heap sort

4 Counting sort

  1. Counting idea
  2. Count array
  3. Output array
  4. Summary - Counting sort

5 Radix sort

  1. Radix idea
  2. Digit pass
  3. Stable sub-sort
  4. Summary - Radix sort

6 Sorting project

  1. Project: Overview
  2. Score array
  3. Apply merge sort
  4. Print statistics

7 Tree

  1. What is a tree?
  2. Node and edge
  3. Binary tree
  4. Summary - Trees

8 Binary search tree

  1. BST rule
  2. BST insert
  3. BST search
  4. Summary - BST

9 AVL tree

  1. Balanced tree
  2. Rotation
  3. Balance after insert
  4. Summary - AVL tree

10 Heap

  1. Min and max heap
  2. Insert
  3. Extract
  4. Summary - Heap

11 Priority queue

  1. What is a priority queue?
  2. Heap-based implementation
  3. Push and pop
  4. Summary - Priority queue

12 Data structures project

  1. Project: Overview
  2. Undo stack
  3. Pending queue
  4. Print the state

13 Graph basics

  1. What is a graph?
  2. Adjacency list
  3. Adjacency matrix
  4. Summary - Graph

14 Breadth-first search

  1. BFS idea
  2. Using a queue
  3. Marking visited
  4. Summary - BFS

15 Depth-first search

  1. DFS idea
  2. Stack or recursion
  3. Backtracking
  4. Summary - DFS

16 Greedy algorithms

  1. Greedy approach
  2. Coin change
  3. Greedy limits
  4. Summary - Greedy

17 Divide and conquer

  1. Three steps
  2. Recursive structure
  3. Master theorem
  4. Summary - Divide and conquer

18 Backtracking

  1. What is backtracking?
  2. State tree
  3. Pruning
  4. Summary - Backtracking

19 Graph project

  1. Project: Overview
  2. City graph
  3. BFS for reachability
  4. Print the result

20 Intermediate final

  1. Challenge 1
  2. Challenge 2
  3. Challenge 3
  4. Challenge 4