Available question text
Count the number of non-empty substrings (in a string of letters 'a'–'j') whose character counts have at most one odd frequency.
Core idea: track a 10-bit parity mask for prefix counts and count pairs of prefixes with equal masks (all even) or masks differing by one bit (one odd) to obtain an O(n) solution.
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Leetcode 1915. Number of Wonderful Substrings
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Source snapshot: Nov 12, 2026
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Uber
Number of Wonderful Substrings
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Source snapshot: Oct 20, 2026
Source frequency score: 57.2. This is not an interview probability.
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