Product

Problem

Given two positive integers a and b, print Even if a * b is even and Odd otherwise.

Approach

A product is odd only when every factor is odd, so the multiplication is unnecessary — a * b is even iff a or b is even. Skipping the product also sidesteps overflow on the variants of this problem with larger bounds.

Complexity

• time: O(1)
• space: O(1)

Code

#include <bits/stdc++.h>
using namespace std;

int main() {
    long long a, b;
    cin >> a >> b;
    cout << ((a % 2 == 1 && b % 2 == 1) ? "Odd" : "Even") << '\n';
}

Notes

Same idea generalises: the product of a list is odd iff no element is even, which is one pass with an early exit.