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Project Euler题解（Problem 2）

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

这道题就是求不超过400万的所有偶斐波那契数的和。很简单。代码如下,主要是通过实现rust胡Iterator Trait来迭代的求出斐波那契数。

#![feature(core)]
use std::iter::Iterator;

// #[derive(Copy)]
struct Fibonacci {
a: u32,
b: u32,
}

impl Fibonacci {
fn new() -> Fibonacci {
Fibonacci{a:0, b:1}
}
}

impl Iterator for Fibonacci {
type Item = u32;
fn next(&mut self) -> Option<u32> {
let result = self.a + self.b;
self.a = self.b;
self.b = result;
Some(result)
}
}

fn solve() -> u32 {
Fibonacci::new().take_while(|&x| x < 4000_000).filter(|&x| x % 2 == 0).sum()
}