Errata & Corrections | Heard In Data Science Interviews (2nd Edition)

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Confirmed Corrections Log

The following errata have been reviewed, verified, and incorporated into subsequent digital revisions and scheduled for the next physical printing.

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Chapter 2: Probability & Statistics • Question 2.114 / Answer 2.114

Math Derivation Confirmed — Next Printing

❌ Original Text: "Solving the system of linear recurrence equations for the random walk across cube vertices yields an expected time of $E[T] = 9$ steps."

✅ Corrected Text: "Solving the system of linear recurrence equations $E_0 = 1 + E_1, \; E_1 = 1 + \frac{2}{3}E_2 + \frac{1}{3}E_0, \; E_2 = 1 + \frac{1}{3}E_3 + \frac{2}{3}E_1$ with absorbing state $E_3 = 0$ yields exactly $E_0 = \mathbf{10\text{ turns}}$."

Note: Fixed in digital update; scheduled for 2nd Edition second printing.

Chapter 9: Computer Science Fundamentals • Question 9.42 / Answer 9.42

Algorithm Complexity Confirmed — Next Printing

❌ Original Text: "The naive recursive approach without memoization exhibits $O(2^n)$ complexity, while the 1D dynamic programming solution runs in $O(n \log n)$ time."

✅ Corrected Text: "The 1D dynamic programming memoization table requires evaluating each prefix in constant time, achieving optimal $\mathbf{O(n)\text{ time}}$ complexity and $O(1)$ auxiliary space."

Note: Typographical correction in the asymptotic complexity summary table.

Chapter 4: Deep Learning & Sequence Models • Question 4.18 / Answer 4.18

Technical Clarification Confirmed — Next Printing

❌ Original Text: "In FlashAttention-2, outer loop blocks over Key/Value blocks $B_c$ while inner loop tiles Query blocks $B_r$."

✅ Corrected Text: "In FlashAttention-2 (Dao, 2023), the loop order is inverted: the outer loop iterates over Query blocks $B_r$ and the inner loop iterates over Key/Value blocks $B_c$, minimizing atomic GPU shared-memory reductions."

Note: Clarified FlashAttention-1 vs FlashAttention-2 loop inversion mechanics.

Chapter 7: Experiment Design & A/B Testing • Question 7.18 / Answer 7.18

Delta Method Formula Confirmed — Next Printing

❌ Original Text: "Applying the first-order Delta Method expansion to ratio metric $R = \bar{Y}/\bar{X}$: $\text{Var}(R) \approx \frac{1}{\mu_X^2}\sigma_Y^2 + \frac{\mu_Y^2}{\mu_X^4}\sigma_X^2 + 2\frac{\mu_Y}{\mu_X^3}\sigma_{XY}$"

✅ Corrected Text: "Applying the first-order Delta Method expansion to ratio metric $R = \bar{Y}/\bar{X}$: $\text{Var}(R) \approx \frac{1}{\mu_X^2}\sigma_Y^2 + \frac{\mu_Y^2}{\mu_X^4}\sigma_X^2 \mathbf{-} 2\frac{\mu_Y}{\mu_X^3}\sigma_{XY}$ (with negative covariance sign)."

Note: Corrected the standard Taylor expansion sign preceding the covariance term.

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