{"id":"canformarray-first-element-keyed-lookup","text":"`canFormArray` indexes pieces by their first element into a dict, enabling O(1) lookup at each position in `arr` — a pattern that recurs in problems with distinctness constraints.","truth_value":"IN","source":"entries/2026/06/06/check-array-formation-through-concatenation-solution.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"created_at":"","updated_at":"","reviewed_at":"","verified_at":"","retracted_at":"","explanation":{"steps":[{"node":"canformarray-first-element-keyed-lookup","truth_value":"IN","reason":"premise"}]}}