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When subproblems nest inside
These signs usually signal interval DP:
1. Operations on ranges. Merging, splitting, or removing contiguous elements.
2. Subproblem independence. Solving [l,k] and [k+1,r] doesn't affect each other.
3. Polynomial complexity hint. Constraints like n≤500 suggest O(n3) is acceptable.
The state is typically dp[l][r] representing the answer for range [l,r].
