4.A - 递推
题目连接 http://acm.hust.edu.cn/vjudge/contest/125308#problem/A
思路: 找规律的题多写几组数。。杨晖三角和二项式定理的应用。二项式定理的系数又与排列组合有关。p[i][j]=(p[i-1][j-1]+p[i][j-1])%1007;
#include<iostream> #include<cstdio> #include<cstring> using namespace std; #define M 2005 int p[M][M]; void jilu() { memset(p,0,sizeof(p)); for(int i=1;i<=2000;i++) { p[1][i]=i%1007; p[i][i]=1; } for(int i=2;i<=2000;i++ )//m行 for(int j=i+1;j<=2000;j++) p[i][j]=(p[i-1][j-1]+p[i][j-1])%1007; } int main() { int t,m,n; scanf("%d",&t); jilu(); while(t--) { scanf("%d %d",&m,&n); printf("%d\n",p[m][n]); } return 0; }