poj2663 递推(填充)

 /*
Time:2019.11.15
Author: Goven
type：递推(填充) 
err:WR 
ref: 其他方法：状态压缩https://blog.csdn.net/u013480600/article/details/19612171 
*/
#include<iostream>
#include<cstring>
using namespace std;

int main()
{
    int n;
    int f[35];
    memset(f, 0, sizeof(f));
    f[0] = 1;//err1 
    f[2] = 3;
    int sum = 3;
    for (int i = 4; i <= 30; i += 2) {
        f[i] = 2 + f[i - 2] + sum * 2;
        sum += f[i];
    }   
    while(cin >> n && n != -1) {
        cout << f[n] << endl;
    }
    return 0;
}

/*
将循环中的sum省略
https://www.cnblogs.com/yu-xing/p/10360698.html 
*/ 
#include<iostream>
#include<cstring>
using namespace std;

int main()
{
    int n;
    int f[35];
    memset(f, 0, sizeof(f));
    f[0] = 1;//err1 
    f[2] = 3;
    for (int i = 4; i <= 30; i += 2) {
        f[i] = (f[i - 2] << 2) - f[i - 4]; 
    }   
    while(cin >> n && n != -1) {
        cout << f[n] << endl;
    }
    return 0;
}