10359

和刚才那道很像，只不过递推公式变了，编为：f(n) = f(n-2)*2+f(n-1);

最坑爹的就是输入0的时候要输出的竟然是1。。。。这也算是一种way。。

//============================================================================
// Name        : 10359.cpp
// Author      : 
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;


char sa[1000], sb[1000], sc[1000];
int n;

void add(char *a, char *b){
	int len1, len2, sans[1000], c;
	char s1[1000], s2[1000], st[1000];
	len1 = strlen(a);
	len2 = strlen(b);
	if(len1 > len2){
		strcpy(st, a);
		strcpy(a, b);
		strcpy(b, st);
	}
	len1 = strlen(a);
	len2 = strlen(b);
	for(int i = 0;i < len1;i++){
		s1[i] = a[len1-1-i];
	}
	s1[len1] = '\0';
	for(int i = 0;i < len2;i++){
		s2[i] = b[len2-1-i];
	}
	s2[len2] = '\0';
	c = 0;
	for(int i = 0;i < len2;i++){
		if(i < len1){
			sans[i] = (s1[i]-'0'+s2[i]-'0'+ c)%10;
			c = (s1[i]-'0'+s2[i]-'0'+ c)/10;
		}
		else{
			sans[i] = (s2[i]-'0'+c)%10;
			c = (s2[i]-'0'+c)/10;
		}
	}
	if(c != 0){
		len2 += 1;
		sans[len2-1] = c;
	}
	for(int i = 0;i < len2;i++){
		sc[i] = sans[len2-1-i]+'0';
	}
	sc[len2] = '\0';
}



int main() {
	freopen("a.txt", "r", stdin);
	while(scanf("%d", &n)!=EOF){
		if(n == 0){
			printf("1\n");
			continue;
		}
		if(n == 1){
			printf("1\n");
			continue;
		}
		if(n == 2){
			printf("3\n");
			continue;
		}
		strcpy(sa, "1");
		strcpy(sb, "3");
		for(int i = 3;i <= n;i++){
			add(sa, sa);
			strcpy(sa, sc);
			add(sa, sb);
			strcpy(sa, sb);
			strcpy(sb, sc);
		}
		printf("%s\n", sc);
	}
	return 0;
}