杨辉三角即组合数的“打表”形式
再求一个二维前缀和
然后处理一下负数即可(因为在求前缀和的过程中有减法)
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 1e3 + 6, P = 19260817;
int t;
ll f[N][N], s[N][N];
int main() {
//杨辉三角
for (int i = 0; i < N; i++) f[i][i] = 1;
for (int i = 0; i < N; i++) f[i][0] = 1;
for (int i = 2; i < N; i++)
for (int j = 1; j < i; j++)
f[i][j] = (f[i-1][j-1] + f[i-1][j]) % P;
//二维前缀和
for (int i = 1; i < N; i++)
for (int j = 1; j < N; j++)
s[i][j] = (s[i-1][j] + s[i][j-1] - s[i-1][j-1] + f[i][j]) % P;
cin >> t;
while (t--) {
int n, m;
cin >> n >> m;
cout << (s[m][n] + P) % P << endl;//注意可能为负数,处理一下即可(不处理貌似只有70)
}
return 0;
}