The Binary Search Pattern
Halve the search space on every comparison. The powerful form in interviews is not searching a sorted array but binary searching the answer itself: guess a value, ask a yes/no feasibility question, and discard half the range of possible answers.
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Interactive problems1
Free to openHow to recognise a binary search problem
The data is sorted or rotated-sorted, or — more often — the answer lies in a numeric range and there is a monotonic feasibility check ("if capacity C works, C+1 also works"). "Minimum capacity to ship packages in D days" is binary search on the answer.
Time and space complexity
O(log n) per search. Binary searching an answer range costs O(log(range) × cost of the feasibility check).
Binary Search practice problems
Each problem pairs a worked explanation with an interactive visualizer you step through yourself, plus the implementation in JavaScript, Python, Java and C++.
Related patterns and concepts
The underlying technique is covered from first principles in the binary search lesson in the DSA visualizer curriculum. Binary Search is one of the 16 coding interview patterns, and its problems also appear in the DSA 75 interview sprint.