Solutions
- https://zxi.mytechroad.com/blog/simulation/leetcode-989-add-to-array-form-of-integer/
- https://zxi.mytechroad.com/blog/graph/leetcode-990-satisfiability-of-equality-equations/
- https://zxi.mytechroad.com/blog/greedy/leetcode-991-broken-calculator/
- https://zxi.mytechroad.com/blog/two-pointers/leetcode-992-subarrays-with-k-different-integers/