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Binary Search

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Binary Search

Binary Search is simple if you keep it on paper. Ananya uses it for folder on disk in a file explorer.

Keep Binary Search small. Ananya should finish folder on disk in a few lines, not a 40-line dump.

Binary Search exists so Ananya can keep folder on disk correct in a file explorer.

Use Binary Search when folder on disk must stay clear. If a simpler DSA step works, use that instead.

If folder on disk breaks under Binary Search, check unbalanced BST becoming a list first.

Place Binary Search next to nearby DSA work — left < root < right is the link.

Close Binary Search with — “If I skip it, folder on disk goes wrong like this: unbalanced BST becoming a list.”

Diagram

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

Exam tip

Board: folder on disk. Dry-run Binary Search. Name the 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 — Ananya uses it for folder on disk in a file explorer.
RuleBinary Search → left < root < right.
RememberBinary Search + time vs memory (a file explorer).
UseBinary Search in a file explorer (folder on disk).
TrapBinary Search — unbalanced BST becoming a list.
ExBinary Search → folder on disk.

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

Example

Short notes

Questions

Binary Search

Example

Short notes

Questions