Repeat-While Loops for Practical Programming

This lecture explains using a repeat-while loop for validating data in an array.

This lecture explains using a 'repeat-while' loop when validating a password.

This lecture discusses converting elements in an array to integer.

We are using repeat while loop to find a cumulative sum threshold.

This lecture will walk you through calculating the sum until it is a single digit.

This lecture explains solving a problem for a coding challenge that involves creating a countdown.

This coding challenge asks us to to find elements in an array that would bring us closer to a target.

This lecture is a little more sophisticated and returns a tuple.

Problem Statement

You’re simulating a device that recharges energy in cycles, starting from a given energy level (between 0 and 100). Each recharge cycle:

• Increases energy by a random amount between 5 and 15.

• Adds 1 second to the recharge time.

• If a recharge causes the energy to exceed 100, the device overheats and the process stops with failure.

• If energy reaches exactly 100, the recharge is successful.

• The process also stops with failure if more than 10 seconds pass without fully charging.

Requirements

• Use a repeat-while loop to control the recharge process.

• Return a result that includes:

  • Whether the recharge succeeded (true) or failed (false)

  • Final energy level

  • Total time elapsed in seconds

  • Recharge history (array of recharge amounts per second)

Coding Challenge: Mission Control: Probe Descent Simulation

Problem Statement

You’re simulating a probe’s descent onto a planetary surface. The goal is to land the probe safely without:

• Running out of fuel

• Crashing due to speed

• Exceeding the maximum number of descent steps

Simulation Rules

• The probe starts at altitude = 500 meters.

• It starts with fuel = 100 units.

• Each second:

  • The probe descends a random amount between 30 and 60 meters.

  • Descent consumes fuel: 1 unit per 5 meters descended (rounded up).

  • The probe’s speed (descent rate) is determined by the most recent descent.

• The mission ends in success if the probe lands (altitude ≤ 0) and its last descent speed is ≤ 40 meters.

• The mission fails if:

  • Fuel runs out before landing.

  • The probe lands but the last descent was too fast (> 40 meters).

  • The simulation runs for more than 10 seconds.

Requirements

• Use a repeat-while loop.

• Return a tuple or struct containing:

  • success: Bool

  • finalAltitude: Int (can be negative)

  • fuelRemaining: Int

  • secondsElapsed: Int

  • history: [(descent: Int, fuelUsed: Int)]

Final Summary

The probe lands successfully if and only if all of the following are true:

• fuel >= 0

• seconds <= 10

• altitude <= 0

• lastDescent <= 40

If any of these conditions are not met, the mission fails.

Coding Challenge: Space Station Oxygen Regulation

Problem Statement

You are simulating an oxygen control system aboard a space station. The station must maintain life-support-safe oxygen levels for a given period of time.

Simulation Rules

• The station starts with oxygen level = 70 units.

• The goal is to maintain oxygen at 50 to 100 units, inclusive, for 15 seconds.

• Each second:

  • Oxygen randomly increases by 0–5 units due to natural air recycling.

  • Oxygen also randomly decreases by 5–15 units due to crew consumption and system leaks.

  • If the oxygen level falls below 50 or exceeds 100, an alert is triggered.

• The station has 3 emergency restores. When triggered:

  • It adds +20 oxygen units immediately, but consumes one restore.

  • Restores are only activated automatically if oxygen would drop below 50.

Failure and Success Criteria

• If the oxygen goes out of safe range (50–100) and no restores remain, the mission fails.

• If the oxygen stays within range or is recovered via restores for all 15 seconds, the mission succeeds.

Requirements

• Use a repeat-while loop.

• Track each second’s oxygen delta and restore usage.

• Return:

  • success: Bool

  • Final oxygen level

  • Seconds elapsed

  • Restores remaining

  • Log of changes: [(second: Int, oxygenBefore: Int, increase: Int, decrease: Int, oxygenAfter: Int, restored: Bool)]

Find First Vowel in a Word

Problem Statement

Write a Swift function that takes a string and returns the first vowel character it encounters, along with its index. If no vowel exists, return nil.

Constraints

• Treat a, e, i, o, u (lowercase only) as vowels.

• You must use a repeat-while loop.

• Do not use for-in, forEach, or high-level iteration methods.

Problem Statement

You’re given a string consisting of digit-letter pairs where each digit (1–9) indicates how many times the following character should appear in the output.

Write a Swift function to expand the string, repeating each character according to its preceding digit.

Requirements

• You must use a repeat-while loop.

• Do not use for-in, forEach, or map, etc.

• The input is well-formed: always an even-length string with digit-letter pairs.

• Return the expanded result as a String.