# Count Number of Balanced Permutations II (LeetCode 3342)

Digit DP / combinatorics: half-sum of digits equals other half.

Practice these follow-ups with [interview copilot app](https://www.linkjob.ai/interview-copilot/) so you rehearse the edge cases before the timer hits.

Key idea: reduce the problem to a known primitive (prefix, heap, or digit DP) and verify with a tiny counterexample.