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hardAdvancedLeetCode#interval DP#fill by length

Burst balloons

Maximize the coins from bursting balloons with an interval DP over which balloon in each range bursts last.

The Runtime Theory Team1 min read
Taught inBottom-up tablesPro — members onlyInstead of recursing and caching, fill an array of answers in an order where every value a cell needs has already been computed. No recursion, no lookups, and the structure of the table becomes visible.
Solve it

Solving happens on the judge — come back and mark it done

Sample cases

innums = [3, 1, 5, 8]

out167

innums = [1, 5]

out10

innums = [5]

out5

Bursting balloon i earns nums[left] × nums[i] × nums[right], where left and right are its current neighbors (1 beyond the ends). Return the maximum coins from bursting all balloons.

Before you code

Choosing which balloon to burst first changes everyone's neighbors, which makes subproblems messy. Choosing which balloon bursts last in a range fixes its neighbors at the range's boundaries and splits the range in two independent halves.

Hints

  1. Pad the array with 1 at both ends.
  2. dp[l][r] is the best for the balloons strictly between l and r.
  3. dp[l][r] = max over k of dp[l][k] + nums[l]*nums[k]*nums[r] + dp[k][r].
  4. Fill by increasing r - l so shorter intervals are ready first. O(n³).

Production & complexity notes

When solving Burst balloons on LeetCode (hard), always state your loop or recursion invariant before writing code. Verify how your chosen data structure behaves on degenerate inputs (single-element inputs, all-duplicate keys, strictly monotonic sequences, or maximum constraint sizes up to $10^5$ elements). In production interviews, pair your implementation with an explicit time and auxiliary space complexity proof, explain why alternative brute-force approaches violate the latency budget, and trace how cache locality and memory allocation overhead affect wall-clock throughput on real hardware. Review the step-by-step memory trace in Bottom-up tables to reinforce the underlying pattern.

What it practices

Choosing a fill order from the dependencies, from Bottom-up tables.

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