1116. Print Zero Even Odd

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1116. Print Zero Even Odd

Description

You have a function printNumber that can be called with an integer parameter and prints it to the console.

  • For example, calling printNumber(7) prints 7 to the console.

You are given an instance of the class ZeroEvenOdd that has three functions: zero, even, and odd. The same instance of ZeroEvenOdd will be passed to three different threads:

  • Thread A: calls zero() that should only output 0‘s.
  • Thread B: calls even() that should only output even numbers.
  • Thread C: calls odd() that should only output odd numbers.

Modify the given class to output the series "010203040506..." where the length of the series must be 2n.

Implement the ZeroEvenOdd class:

  • ZeroEvenOdd(int n) Initializes the object with the number n that represents the numbers that should be printed.
  • void zero(printNumber) Calls printNumber to output one zero.
  • void even(printNumber) Calls printNumber to output one even number.
  • void odd(printNumber) Calls printNumber to output one odd number.

Example 1:

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Input: n = 2
Output: "0102"
Explanation: There are three threads being fired asynchronously.
One of them calls zero(), the other calls even(), and the last one calls odd().
"0102" is the correct output.

Example 2:

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Input: n = 5
Output: "0102030405"

Constraints:

  • 1 <= n <= 1000

Hints/Notes

  • 2025/03/24 Q3
  • concurrency
  • No solution from 0x3F or Leetcode

Solution

Language: C++

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class ZeroEvenOdd {
private:
    mutex m;
    condition_variable cv;
    int cur, printZero;
    int n;

public:
    ZeroEvenOdd(int n) {
        this->n = n;
        this->cur = 1;
        this->printZero = 0;
    }

    // printNumber(x) outputs "x", where x is an integer.
    void zero(function<void(int)> printNumber) {
        while (true) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&]{
                return !printZero || cur > n;
            });
            if (cur > n) {
                return;
            }
            printNumber(0);
            printZero ^= 1;
            cv.notify_all();
        }
    }

    void even(function<void(int)> printNumber) {
        while (true) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&]{
                return (printZero && cur % 2 == 0) || cur > n;
            });
            if (cur > n) {
                return;
            }
            printNumber(cur);
            cur++;
            printZero ^= 1;
            cv.notify_all();
        }
    }

    void odd(function<void(int)> printNumber) {
        while (true) {
            unique_lock<mutex> lock(m);
            cv.wait(lock, [&]{
                return (printZero && cur % 2) || cur > n;
            });
            if (cur > n) {
                return;
            }
            printNumber(cur);
            cur++;
            printZero ^= 1;
            cv.notify_all();
        }
    }
};