DSA · Theory

Binary Search

Theory

46/810

Binary Search

Binary Search is a DSA topic. In plain words you use it for folder on disk in a file explorer. Don’t start with a slogan — start with that picture.

Smallest example: left < root < right. Type it, run it, and say what you see. If you can do that from memory, you know Binary Search.

From the example next to this theory — Binary search halves a sorted array each step — O(log n).

Trap — unbalanced BST becoming a list. Fix that before you talk about advanced DSA.

Viva — what is Binary Search? Then show left < root < right. Then name the trap.

Diagram

  [2, 5, 8, 12, 20]  find 12
         mid=8 → right
              mid=12 found

Exam tip

What is Binary Search? Show this: left < root < right. Trap: unbalanced BST becoming a list.

Example

def binary_search(arr, target):
    lo, hi = 0, len(arr) - 1
    while lo <= hi:
        mid = (lo + hi) // 2
        if arr[mid] == target:
            return mid
        if arr[mid] < target:
            lo = mid + 1
        else:
            hi = mid - 1
    return -1

print(binary_search([1, 3, 5, 7, 9], 7))

Binary search halves a sorted array each step — O(log n).

Short notes

DefBinary Search — folder on disk in a file explorer.
Ruleleft < root < right
Trapunbalanced BST becoming a list
Usea file explorer

DSA · Theory

Binary Search

← All stacks

Theory

46/810

Binary Search

Binary Search is a DSA topic. In plain words you use it for folder on disk in a file explorer. Don’t start with a slogan — start with that picture.

Smallest example: left < root < right. Type it, run it, and say what you see. If you can do that from memory, you know Binary Search.

From the example next to this theory — Binary search halves a sorted array each step — O(log n).

Trap — unbalanced BST becoming a list. Fix that before you talk about advanced DSA.

Viva — what is Binary Search? Then show left < root < right. Then name the trap.

Diagram

  [2, 5, 8, 12, 20]  find 12
         mid=8 → right
              mid=12 found

Exam tip

What is Binary Search? Show this: left < root < right. Trap: unbalanced BST becoming a list.

Example

def binary_search(arr, target):
    lo, hi = 0, len(arr) - 1
    while lo <= hi:
        mid = (lo + hi) // 2
        if arr[mid] == target:
            return mid
        if arr[mid] < target:
            lo = mid + 1
        else:
            hi = mid - 1
    return -1

print(binary_search([1, 3, 5, 7, 9], 7))

Binary search halves a sorted array each step — O(log n).

Short notes

DefBinary Search — folder on disk in a file explorer.
Ruleleft < root < right
Trapunbalanced BST becoming a list
Usea file explorer

Binary Search

Example

Short notes

Questions

Binary Search

Example

Short notes

Questions