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20 Binary Search Problems To Revise Before Interviews

· 5 min read

I've curated 20 binary search problems that teach you all major patterns. These aren't random problems, they're specifically chosen to build your intuition for spotting binary search problems.

🎯 The 20 Essential Problems​

1. Binary Search - LeetCode 704

  • Pattern: Basic binary search template
  • Why: Foundation - must be able to code this in sleep
  • Companies: Everyone asks this as warmup

2. Search in Rotated Sorted Array - LeetCode 33

  • Pattern: Binary search with modified condition
  • Why: Tests ability to adapt binary search logic
  • Companies: Amazon, Microsoft, Meta, Apple, Google

3. Find Minimum in Rotated Sorted Array - LeetCode 153

  • Pattern: Finding pivot point
  • Why: Variation where you're not searching for target
  • Companies: Amazon, Microsoft, Bloomberg

Pattern 2: Binary Search on Answer Space​

4. Koko Eating Bananas - LeetCode 875

  • Pattern: Binary search on answer space
  • Why: Classic example of searching for minimum feasible value
  • Companies: Google, Meta, Amazon

5. Minimum Number of Days to Make m Bouquets - LeetCode 1482

  • Pattern: Binary search on days/time
  • Why: Teaches feasibility checking pattern
  • Companies: Amazon, Google

6. Capacity To Ship Packages Within D Days - LeetCode 1011

  • Pattern: Binary search on capacity/size
  • Why: Shows binary search on continuous resource constraints
  • Companies: Amazon, Google, Meta

7. Split Array Largest Sum - LeetCode 410

  • Pattern: Minimize maximum value
  • Why: Hard problem that becomes easy with binary search mindset
  • Companies: Google, Meta, ByteDance

8. Minimum Limit of Balls in a Bag - LeetCode 1760

  • Pattern: Minimize penalty with operations
  • Why: Non-obvious binary search application
  • Companies: Amazon, Google

9. Magnetic Force Between Two Balls - LeetCode 1552

  • Pattern: Maximize minimum distance
  • Why: Teaches binary search on distance/spacing
  • Companies: Google, Amazon

Pattern 3: Binary Search on Value Range​

10. Kth Smallest Element in a Sorted Matrix - LeetCode 378

  • Pattern: Binary search on value range
  • Why: Shows counting elements ≤ mid approach
  • Companies: Google, Amazon, Meta

Pattern 4: Binary Search with Two Pointers​

11. Find K Closest Elements - LeetCode 658

  • Pattern: Binary search for starting position
  • Why: Combination of binary search and sliding window
  • Companies: Meta, Amazon, Google

12. 3Sum Closest - LeetCode 16

  • Pattern: Sort + fix one element + binary search/two pointers
  • Why: Shows when to combine patterns
  • Companies: Amazon, Microsoft, Bloomberg

Pattern 5: Finding Boundaries​

13. Find First and Last Position of Element in Sorted Array - LeetCode 34

  • Pattern: Finding boundaries with binary search
  • Why: Must know how to find leftmost and rightmost occurrence
  • Companies: Amazon, Meta, Microsoft, Apple

14. Search a 2D Matrix II - LeetCode 240

  • Pattern: Binary search in 2D space
  • Why: Shows search space reduction technique
  • Companies: Amazon, Google, Meta, Apple

Pattern 7: Binary Search on Unsorted Arrays​

15. Find Peak Element - LeetCode 162

  • Pattern: Binary search without full sorting
  • Why: Shows binary search works even in unsorted arrays with properties
  • Companies: Meta, Google, Microsoft, Bloomberg

16. Single Element in a Sorted Array - LeetCode 540

  • Pattern: Binary search with parity checking
  • Why: Clever application of binary search on paired elements
  • Companies: Amazon, Google

17. Median of Two Sorted Arrays - LeetCode 4

  • Pattern: Binary search for partition point
  • Why: One of the hardest binary search problems, ultimate test
  • Companies: Google, Amazon, Meta, Apple, Microsoft

18. Find the Duplicate Number - LeetCode 287

  • Pattern: Binary search on value with counting
  • Why: Non-obvious binary search application
  • Companies: Amazon, Microsoft, Meta

19. Sqrt(x) - LeetCode 69

  • Pattern: Binary search on result space
  • Why: Simple but teaches searching for mathematical answer
  • Companies: Amazon, Microsoft, Bloomberg

20. Valid Perfect Square - LeetCode 367

  • Pattern: Binary search for exact match
  • Why: Variation of sqrt problem
  • Companies: Amazon, LinkedIn

💡 Key Insights​

  1. Sorted array - Classic binary search
  2. Search space is monotonic - Answer gets better/worse in one direction
  3. "Minimum/Maximum" + "feasible/possible" - Binary search on answer
  4. Finding boundaries - First/last occurrence

Common Templates:​

Template 1: Finding Exact Value

left, right = 0, len(arr) - 1
while left <= right:
    mid = (left + right) // 2
    if arr[mid] == target:
        return mid
    elif arr[mid] < target:
        left = mid + 1
    else:
        right = mid - 1

Template 2: Finding Boundary

left, right = 0, len(arr)
while left < right:
    mid = (left + right) // 2
    if condition(mid):
        right = mid
    else:
        left = mid + 1

Template 3: Binary Search on Answer

left, right = min_answer, max_answer
while left < right:
    mid = (left + right) // 2
    if is_feasible(mid):
        right = mid
    else:
        left = mid + 1

📚 Study Plan​

Day 1-3: Master classic binary search (Problems 1-3) Day 4-7: Binary search on answer space (Problems 4-9) Day 8-10: Advanced patterns (Problems 10-16) Day 11-14: Hard problems and edge cases (Problems 17-20)

Remember: The key to binary search is identifying when a problem has a monotonic property that can be exploited!