LLDHub
Problems·ATM Machine
L3 · Medium

ATM Machine

Problem

Design an ATM system that handles card authentication, balance inquiry, cash withdrawal, and deposit operations.

Requirements

  • Card insertion and PIN authentication (max 3 attempts)
  • Check account balance
  • Withdraw cash (check balance + dispense notes)
  • Deposit cash
  • Transfer funds between accounts
  • Eject card and end session

Constraints

  • After 3 wrong PIN attempts, block the card
  • ATM has limited cash — track denomination counts
  • Minimum withdrawal: ₹500, Maximum: ₹20,000
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