{"id":"triangular-number-correctness","text":"A run of `n` identical characters contributes exactly `n*(n+1)/2` single-character substrings, and the integer division is always exact because one of `n` or `n+1` is even","truth_value":"IN","source":"entries/2026/06/06/count-substrings-with-only-one-distinct-letter-solution.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"created_at":"","updated_at":"","reviewed_at":"","verified_at":"","retracted_at":"","explanation":{"steps":[{"node":"triangular-number-correctness","truth_value":"IN","reason":"premise"}]}}