HDOJ 1028 Ignatius and the Princess III(递推)
Problem Description
“Well, it seems the first problem is too easy. I will let you know how foolish you are later.” feng5166 says.
“The second problem is, given an positive integer N, we define an equation like this:
N=a[1]+a[2]+a[3]+…+a[m];
a[i]>0,1<=m<=N;
My question is how many different equations you can find for a given N.
For example, assume N is 4, we can find:
4 = 4;
4 = 3 + 1;
4 = 2 + 2;
4 = 2 + 1 + 1;
4 = 1 + 1 + 1 + 1;
so the result is 5 when N is 4. Note that “4 = 3 + 1” and “4 = 1 + 3” is the same in this problem. Now, you do it!”
Input
The input contains several test cases. Each test case contains a positive integer N(1<=N<=120) which is mentioned above. The input is terminated by the end of file.
Output
For each test case, you have to output a line contains an integer P which indicate the different equations you have found.
Sample Input
4
10
20
Sample Output
5
42
627
思路:
(i,j)(i>=j)代表的含义是i为n,j为划分的最大的数字。
边界:a(i,0) = a(i, 1) = a(0, i) = a(1, i) = 1;
i|j==0时,无论如何划分,结果为1;
当(i>=j)时,
划分为{j,{x1,x2…xi}},{x1,x2,…xi}的和为i-j,
{x1,x2,…xi}可能再次出现j,所以是(i-j)的j划分,所以划分个数为a(i-j,j);
划分个数还需要加上a(i,j-1)(累加前面的);
当(i < j)时,
a[i][j]就等于a[i][i];
import java.util.Scanner;
public class Main{
static int a[][] = new int[125][125];
public static void main(String[] args) {
dabiao();
Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
int n = sc.nextInt();
System.out.println(a[n][n]);
}
}
private static void dabiao() {
for(int i=0;i<121;i++){
a[i][0]=1;
a[i][1]=1;
a[0][i]=1;
a[1][i]=1;
}
for(int i=2;i<121;i++){
for(int j=2;j<121;j++){
if(j<=i){
a[i][j]=a[i][j-1]+a[i-j][j];
}else{
a[i][j]=a[i][i];
}
}
}
}
}
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