题解 | 二维斐波那契数列

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int a = in.nextInt();
            int b = in.nextInt();
            System.out.println(f(a, b));
        }
    }
    public static int f(int a, int b) {
        if (a < 1 || b < 1) return 0;

        long[][] dp = new long[a + 1][b + 1];
        dp[1][1] = 1;

        for (int i = 1; i <= a; i++) {
            for (int j = 1; j <= b; j++) {
                if (i == 1 && j == 1) {
                    dp[i][j] = 1;
                } else {
                    dp[i][j] = (dp[i - 1][j] + dp[i][j - 1]) % 1000000007;
                }
            }
        }

        return (int)dp[a][b];
    }


}