n划分为1，2，3等等（动态规划）

package bd_algo;

import java.util.Scanner;

public class coin {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int[] coins = {0, 1, 2, 3};
while (in.hasNext()) {
int n = in.nextInt();
int[][] dp = new int[coins.length][n + 1];
for (int i = 1; i < coins.length; i++) {
for (int j = 0; j < n + 1; j++) {
if (j == 0) {
dp[i][j] = 1;
continue;
}
if(j - coins[i] >= 0) {
dp[i][j] = dp[i][j - coins[i]] + dp[i - 1][j];
}else {
dp[i][j] = dp[i -1 ][j];
}
}
}
System.out.println(dp[3]
);
}
}
}