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Hosting code and solutions for problems to help prepare for data science jobs.

Please contribute! Feel free to place notebooks or example code under the topics directory.

Suggested weekly topics:

Week 1 — Python Coding Drills

  • Arrays, strings, dicts, complexity, and edge-case thinking.
  • LeetCode-style problem practice (1D/2D arrays, maps, string ops).
  • Quick runtime analysis and Python idioms for speed.

Week 2 — Basic Probability & Counting

  • Sample spaces, independence, conditional probability.
  • Counting problems, permutations/combinations, inclusion-exclusion.
  • Problems: dice, cards, and urn draws.
  • Introduce Bayes’ theorem intuitively.

Week 3 — Random Variables & Expectation

  • Discrete distributions (Bernoulli, Binomial, Geometric, Poisson).
  • Continuous distributions (Uniform, Exponential).
  • Expected value, variance, and linearity of expectation.
  • Simulation sanity checks in Python.

Week 4 — Joint, Marginal & Conditional Distributions

  • Covariance and correlation.
  • Conditional expectation and independence.
  • Problems: covariance between dice rolls, correlation interpretation.

Week 5 — Inference & Hypothesis Testing

  • Z-test vs t-test, Type I/II errors, p-values, statistical power.
  • Coin fairness, A/B test examples.
  • Practice designing simple hypothesis tests from data.

Week 6 — Sampling, LLN & CLT

  • Law of Large Numbers and Central Limit Theorem.
  • Confidence intervals and bootstrapping intuition.
  • Applying CLT to A/B testing, conversion rate differences.

Week 7 — Linear Models & Loss Functions

  • Linear regression derivation, least squares, gradient descent intuition.
  • Regularization (L1, L2), bias-variance tradeoff.
  • Derive closed-form and interpret coefficients.

Week 8 — Classification, Metrics, and Probabilistic Thinking

  • Logistic regression, likelihood and log-odds.
  • Evaluation metrics: accuracy, precision/recall, ROC-AUC.
  • Calibrated probabilities, confusion matrix reasoning.

Week 9 — Model Selection, Validation, and Overfitting

  • Cross-validation, time-series split, learning curves.
  • AIC/BIC, early stopping.
  • Feature leakage and robust validation under realistic constraints.

Week 10 — Python Data Structures & Coding Review

  • Mixed interview problems: data parsing, simulation, aggregation.
  • Quick review of time/space tradeoffs.
  • Writing clean, testable code under interview conditions.

Week 11 — SQL & Data Manipulation

  • Aggregation queries, joins, subqueries, window functions.
  • Real-world examples: churn rate, top-N users, retention tables.
  • Optimization mindset: when to use GROUP BY vs window.

Week 12 — Case Study & Full Integration

  • End-to-end mock interviews:
    • Prob/stat + ML + code in one session.
    • E.g., design an A/B test → analyze → interpret model results.
  • Reflection: what to keep improving weekly.

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Hosting problems and solutions for data science jobs

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