第二题我用排列组合写了下 package tencent; import java.util.Scanner; public class Dpstrk{          public static void main(String[] args){                  Scanner scan = new Scanner(System.in);         int k = scan.nextInt();         int a = scan.nextInt();         int x = scan.nextInt();         int b = scan.nextInt();         int y = scan.nextInt();                  System.out.print(getInt(k, a, x, b, y));         scan.close();     }          public static int  getInt(int k,int a,int x,int b,int y){         int d=0;         int count = 0;         if(a*x<k)               d = x;         else              d = k/a;// 歌曲A的个数         for(int i =0;i<=d;i++){             int cb = (k-i*a)/b;             if(cb>y||(k-i*a)%b !=0)//注意y的选择和整除                 continue;             count += (getjs(x)/(getjs(i)*getjs(x-i))* getjs(y)/(getjs(cb)*getjs(y-cb)))%1000000007;         }                  return count;     }          public static int getjs(int n){         if(n==0)              return 1;         int cj = 1;         for(int i=1;i<=n;i++){                          cj *= i;         }         return cj;              } }