- Wrong tree size: Segment tree needs up to n nodes for safety. 2n might not suffice for all indices.
- Incorrect range handling: Off-by-one errors in range queries are common. Carefully define inclusive/exclusive bounds.
- Forgetting to propagate lazy updates: With lazy propagation, must push updates down before querying children.
- Integer overflow in sums: Large arrays with large values can overflow.
Use long integers.