杭电1005

输入A B n ，f(1) = 1, f(2) = 1, f(n) = (A * f(n - 1) + B * f(n - 2)) mod 7
难点：1.题目n会达到10亿，如果单纯用递归，空间不够用，所以得发现规律
#include<iostream>
using namespace std;
int f(int a, int b, int n)
{
    if (n == 1 || n == 2)
        return 1;
    else
        return (a*f(a, b, n - 1) + b*f(a, b, n - 2))%7;
}
int  main( )
{
    int a, b, n;
    cin >> a >> b >> n;
    while (a!=0 || b!=0 || n!=0)
    {
        n = n % 49;
        cout << f(a, b, n)<<endl;
        cin >> a >> b >> n;
    }
    return 0;
}

转载于:https://www.cnblogs.com/chendashennihao/p/5361303.html