Find the Index of the First Occurrence

Easy
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Solution Guide: Find the Index of the First Occurrence

Approach

Try every possible starting index in haystack where needle could fit and compare characters sequentially.

Complexity Analysis

Time
O(n * m)
Space
O(1)

Pattern

String Scan (Brute Force)

Why It Works

Any valid match must start at one of these positions, so checking each candidate start guarantees the first occurrence is found.

Updated Feb 2026