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const std = @import("std");
pub fn factorial(n: u64) u64 {
if (n == 0) return 1;
return n * factorial(n - 1);
}
pub fn isPrime(n: u64) bool {
if (n < 2) return false;
if (n == 2) return true;
if (n % 2 == 0) return false;
var i: u64 = 3;
while (i * i <= n) : (i += 2) {
if (n % i == 0) return false;
}
return true;
}
pub fn gcd(a: u64, b: u64) u64 {
var x = a;
var y = b;
while (y != 0) {
const t = y;
y = x % y;
x = t;
}
return x;
}
// ── Tests with "math: " prefix ────────────────────────────────────────────────
// Run all: zig build test
// Run math only: zig build test -- --test-filter "math:"
test "math: factorial base cases" {
try std.testing.expectEqual(@as(u64, 1), factorial(0));
try std.testing.expectEqual(@as(u64, 1), factorial(1));
try std.testing.expectEqual(@as(u64, 2), factorial(2));
}
test "math: factorial larger values" {
try std.testing.expectEqual(@as(u64, 120), factorial(5));
try std.testing.expectEqual(@as(u64, 5040), factorial(7));
try std.testing.expectEqual(@as(u64, 3628800), factorial(10));
}
test "math: isPrime small primes" {
try std.testing.expect(isPrime(2));
try std.testing.expect(isPrime(3));
try std.testing.expect(isPrime(5));
try std.testing.expect(isPrime(97));
}
test "math: isPrime composites and edge cases" {
try std.testing.expect(!isPrime(0));
try std.testing.expect(!isPrime(1));
try std.testing.expect(!isPrime(4));
try std.testing.expect(!isPrime(100));
}
test "math: gcd basics" {
try std.testing.expectEqual(@as(u64, 6), gcd(12, 18));
try std.testing.expectEqual(@as(u64, 1), gcd(7, 13));
try std.testing.expectEqual(@as(u64, 5), gcd(5, 0));
try std.testing.expectEqual(@as(u64, 5), gcd(0, 5));
}
// Deliberately named differently — filtered OUT by "--test-filter math:"
test "number theory: Euclid handles equal inputs" {
try std.testing.expectEqual(@as(u64, 42), gcd(42, 42));
}
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