mediumLeetCode#dynamic-programming#strings

Longest Common Subsequence

Return the longest sequence length shared by two strings in order, not necessarily contiguously.

The Runtime Theory TeamSeptember 25, 202625 min read

Solve it

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Sample cases

intext1="abcde", text2="ace"

out3

intext1="abc", text2="abc"

out3

intext1="abc", text2="def"

out0

Return the longest sequence length shared by two strings in order, not necessarily contiguously.

A good solution should

State the invariant or decision rule that makes the approach correct.
Explain time and space costs in terms of input size and required output.
Handle empty, minimal, duplicate, and boundary-shaped inputs.

Reasoning prompt

Use a state over string prefixes. Matching trailing characters extend the diagonal; otherwise discard one trailing character.

Use the linked judge for the canonical challenge. The examples above are compact TRT checks; create additional tests around the boundary most likely to break your invariant.

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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A good solution should

Reasoning prompt

More practice in this topic

One dispatch a week