fjnu 1151 Adding 1s, 2s, and 3s

Description

Integer 4 can be expressed as a sum of 1s, 2s, and 3s in seven different ways as follows:

Write a program that determines the number of ways in which a given integer can be expressed as a sum of 1s, 2s, and 3s. You may assume that the integer is positive and less than 20.

Input

The input consists of T test cases. The number of test cases (T ) is given in the first line of the input file. Each test case consists of an integer written in a single line.

Output

Print exactly one line for each test case. The line should contain an integer representing the number of ways.

Sample Input

3
4
7
10

Sample Output

7
44
274

 

KEY:这个题我一开始以为要什么算法呢……后来写了几项发现原来有规律……f[i]=f[i-1]+f[i-2]+f[i-3];

 

Source:

 #include<iostream>
using namespace std;

int f[25]=...{1,1,2};

void GetList()
...{
    for(int i=3;i<25;i++)
        f[i]=f[i-1]+f[i-2]+f[i-3];
}

int main()
...{
    GetList();
    int N;
    int n;
    cin>>N;
    for(int i=1;i<=N;i++)
    ...{
        cin>>n;
        cout<<f[n]<<endl;
    }
    return 0;
}