题解 | 小红走矩阵

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        final long MOD = 998244353;
        Scanner in = new Scanner(System.in);

        int n = in.nextInt();
        int m = in.nextInt();

        long[][] dp = new long[n+1][m+1];

        for (int i = 1; i <= n; i++) {
            dp[i][1] = 1;
        }
        for (int j = 1; j <= m; j++) {
            dp[1][j] = 1;
        }

        for (int i = 2; i <= n; i++) {
            for (int j = 2; j <= m; j++) {
                dp[i][j] = (dp[i - 1][j] + dp[i][j - 1]) % MOD;
            }
        }

        System.out.println(dp[n][m]);

    }
}