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const std = @import("std");
/// Compute the nth Fibonacci number iteratively.
pub fn fibonacci(n: u64) u64 {
if (n <= 1) return n;
var a: u64 = 0;
var b: u64 = 1;
var i: u64 = 2;
while (i <= n) : (i += 1) {
const next = a + b;
a = b;
b = next;
}
return b;
}
pub fn main(init: std.process.Init) !void {
const io = init.io;
var buf: [4096]u8 = undefined;
var fw: std.Io.File.Writer = .init(.stdout(), io, &buf);
defer fw.interface.flush() catch {};
const w = &fw.interface;
try w.print("Fibonacci sequence (first 12 terms):\n", .{});
for (0..12) |n| {
try w.print(" fib({d}) = {d}\n", .{ n, fibonacci(n) });
}
}
test "fibonacci base cases" {
try std.testing.expectEqual(@as(u64, 0), fibonacci(0));
try std.testing.expectEqual(@as(u64, 1), fibonacci(1));
try std.testing.expectEqual(@as(u64, 1), fibonacci(2));
}
test "fibonacci sequence" {
const expected = [_]u64{ 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 };
for (expected, 0..) |v, n| {
try std.testing.expectEqual(v, fibonacci(n));
}
}
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