题解 | 斐波那契数列 c#

using System;
using System.Collections.Generic;
using System.Linq;
public class Program {
    public static void Main() {
        int.TryParse(Console.ReadLine(), out int n);
        Console.WriteLine(FibonacciSequence(n));
    }
        public static long FibonacciSequence(long num)
    {
        long dp = 0;
        if(num <= 2)
        {
            return num;
        }
        else
        {
            //这个斐波那契数列的输入数非常大，直接用递归一定超时，用动态规划
            long a =1; //f(1)
            long b =1; //f(2)
            
            const long INF = 1000_000_007L;

            for (int i = 3; i <= num; i++)
            {
                dp = (a + b)%INF;
                a = b;
                b = dp;
            }
            return dp;
        }
        
    }
}