Count Binary Substrings

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Solution Guide: Count Binary Substrings

Approach

Compress the string into run lengths of consecutive equal characters and add the minimum of each adjacent run pair.

Complexity Analysis

Time
O(n)
Space
O(1)

Pattern

Run-Length Grouping

Why It Works

A valid substring across a 0/1 boundary can use at most the shorter adjacent run length.

Updated Feb 2026