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https://github.com/ziglang/zig.git
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49 lines
1.5 KiB
Zig
49 lines
1.5 KiB
Zig
//! Greatest common divisor (https://mathworld.wolfram.com/GreatestCommonDivisor.html)
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const std = @import("std");
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const expectEqual = std.testing.expectEqual;
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/// Returns the greatest common divisor (GCD) of two unsigned integers (a and b) which are not both zero.
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/// For example, the GCD of 8 and 12 is 4, that is, gcd(8, 12) == 4.
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pub fn gcd(a: anytype, b: anytype) @TypeOf(a, b) {
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// only unsigned integers are allowed and not both must be zero
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comptime switch (@typeInfo(@TypeOf(a, b))) {
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.Int => |int| std.debug.assert(int.signedness == .unsigned),
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.ComptimeInt => {
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std.debug.assert(a >= 0);
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std.debug.assert(b >= 0);
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},
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else => unreachable,
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};
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std.debug.assert(a != 0 or b != 0);
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// if one of them is zero, the other is returned
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if (a == 0) return b;
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if (b == 0) return a;
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// init vars
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var x: @TypeOf(a, b) = a;
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var y: @TypeOf(a, b) = b;
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var m: @TypeOf(a, b) = a;
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// using the Euclidean algorithm (https://mathworld.wolfram.com/EuclideanAlgorithm.html)
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while (y != 0) {
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m = x % y;
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x = y;
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y = m;
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}
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return x;
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}
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test "gcd" {
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try expectEqual(gcd(0, 5), 5);
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try expectEqual(gcd(5, 0), 5);
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try expectEqual(gcd(8, 12), 4);
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try expectEqual(gcd(12, 8), 4);
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try expectEqual(gcd(33, 77), 11);
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try expectEqual(gcd(77, 33), 11);
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try expectEqual(gcd(49865, 69811), 9973);
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try expectEqual(gcd(300_000, 2_300_000), 100_000);
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try expectEqual(gcd(90000000_000_000_000_000_000, 2), 2);
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}
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