Practice · 1 of 3

Balanced Sequences

CHALLENGE

Difficulty: advanced+25 XP

**Problem.** Line 1: q. Each line: n. Print the number of balanced sequences of n pairs of brackets mod 1e9+7. **Constraints:** 1 ≤ q ≤ 500000; 1 ≤ n ≤ 500000. Factorial precompute + the Catalan identity; the O(n^2) recurrence W cannot finish.

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