Last Hour Cheat Sheet
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Last-Hour Cheat Sheet

Read this once before the test. Do not try to learn new theory now.

Aptitude

  • Net successive percent change: a + b + ab/100 for two increases; a āˆ’ b āˆ’ ab/100 for increase then decrease.
  • Average = total/count. Rebuild total after adding/removing a value.
  • Work: add rates, not days.
  • Equal-distance average speed = 2xy/(x+y).
  • Train: convert km/h to m/s using 5/18.
  • Probability: at least one = 1 āˆ’ none.
  • Unit digits repeat in cycles.
  • Neither/either usually take singular verb in standard tests.
  • Use a/an by sound: a university, an honest person.
  • Syllogism: never reverse "All A are B."

Technical

  • Queue FIFO, stack LIFO, hash lookup average O(1).
  • BFS queue/unweighted shortest path; DFS stack/recursion.
  • Binary search needs sorted input.
  • Merge sort O(n log n), stable; quicksort worst O(nĀ²).
  • Process own memory; thread shares process memory.
  • Page fault = page absent from RAM.
  • Deadlock: mutual exclusion, hold-wait, no preemption, circular wait.
  • TCP reliable; UDP connectionless.
  • DNS 53, HTTP 80, HTTPS 443, SSH 22, DHCP 67/68.
  • /27 = 30 traditional usable hosts.
  • ARP IP to MAC; DNS name to IP; DHCP IP settings.
  • ADC analogue to digital; watchdog resets hang; I2C two-wire.
  • Waterfall sequential; Agile iterative; sprint = time box.
  • Regression = old features after a change; retesting = confirm particular fix.

Pseudocode

  • Write a variable table.
  • MOD = remainder; DIV = integer quotient.
  • WHILE can run zero times; REPEAT runs at least once.
  • Update values line by line in order.
  • ELSE goes to nearest unmatched IF.
  • State recursion base case.
  • Loop doubling/halving is O(log n).

Coding

  • Read constraints first.
  • Secure the easiest problem first.
  • Test n=0/1 if allowed, duplicates, negatives, extremes.
  • Sum/max/count: one scan.
  • Frequency/pair: hash map.
  • Sorted pair/palindrome: two pointers.
  • Balanced brackets: stack.
  • Shortest unweighted grid: BFS.

Games

  • Tutorial first; no random clicking.
  • Motion: plan path backward from target.
  • Grid: chunk locations/order.
  • Switch: use feedback to eliminate possibilities.
  • Digit: estimate, then calculate.

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