The Runtime Theory
mediumLeetCode#linked-lists#carry

Add Two Numbers

Add two nonnegative integers whose digits are stored in reverse order in linked lists.

The Runtime Theory Team25 min read
Solve it

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

Sample cases

inl1=[2,4,3], l2=[5,6,4]

out[7,0,8]

inl1=[0], l2=[0]

out[0]

inl1=[9,9,9], l2=[1]

out[0,0,0,1]

Add two nonnegative integers whose digits are stored in reverse order in linked lists.

A good solution should

  • State the invariant or decision rule that makes the approach correct.
  • Explain the time and space complexity in terms of the input sizes and required output.
  • Handle empty, minimal, duplicate, and boundary-shaped inputs covered by the contract.

Reasoning prompt

Process nodes while either list or a final carry remains. Preserve leading zero behavior according to the input contract.

Use the linked judge for the canonical problem. The examples above are compact TRT checks; write additional cases before submitting, especially for the boundary that tends to break your chosen invariant.

More practice in this topic

medium · linked listsCopy List with Random Pointermedium · linked listsFind the Duplicate Numbereasy · linked listsLinked List Cycle

One dispatch a week

The trace behind each problem, the tradeoff that explains it, and one technical dispatch per week — no noise.

One technical dispatch per week. No noise.

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