What is the time and space complexity of Find First and Last Position?

Time complexity: O(log n). Space complexity: O(1).

Find First and Last Position

Med

Concept

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Solution Guide: Find First and Last Position

Approach

Run binary search twice. The first search is left-biased: when it finds the target, it records the index and keeps searching left. The second is right-biased and keeps searching right. Together they find both boundaries.

Complexity Analysis

Time: O(log n)
Space: O(1)

Pattern

Binary Search (Boundary Finding)

Why It Works

Running binary search twice with different bias — left-biased continues searching left even after finding a match to find the first occurrence, right-biased does the opposite.

Updated Feb 2026