#pragma mark -- 斐波那契數(shù)列 求第n個斐波那契數(shù)
- (NSInteger)fib:(NSInteger)n {
    if (n <= 1) {
        return n;
    }
    NSInteger first = 0;
    NSInteger second = 1;
    NSLog(@"0 \n1");
    while (n -- > 1) {//n>=1 同時n--
        second += first;//fib(2) = fib(1) + fib(0);
        first = second - first;//first = 原來的second fib(1) = 現(xiàn)在的second fib(2) - 原來的first fib(0)
        NSLog(@"%ld",second);
    }
    return second;
}