2023-02-11：给你两个整数 m 和 n 。构造一个 m x n 的网格，其中每个单元格最开始是白色， 请你用 红、绿、蓝 三种颜色为每个单元格涂色。所有单元格都需要被涂色， 涂色方案需要满足：

use std::iter::repeat;fn main() {    let ans3 = color_the_grid(4, 3);    println!("ans3 = {}", ans3);}
static MOD: i32 = 1000000007;
fn color_the_grid(m: i32, n: i32) -> i32 {    let status = 1 << (m << 1);    let mut dp: Vec<Vec<Vec<i32>>> = repeat(        repeat(repeat(-1).take(status as usize).collect())            .take(m as usize)            .collect(),    )    .take(n as usize)    .collect();    return process(0, 0, 0, n, m, &mut dp);}
fn process(i: i32, j: i32, s: i32, n: i32, m: i32, dp: &mut Vec<Vec<Vec<i32>>>) -> i32 {    if i == n {        return 1;    }    if j == m {        return process(i + 1, 0, s, n, m, dp);    }    if dp[i as usize][j as usize][s as usize] != -1 {        return dp[i as usize][j as usize][s as usize];    }    let up = (s >> (j * 2)) & 3;    let left = if j == 0 { 0 } else { (s >> ((j - 1) << 1)) & 3 };    let mut ans = 0;    if up != 1 && left != 1 {        ans += process(i, j + 1, (s ^ (up << (j * 2))) | (1 << (j * 2)), n, m, dp);        ans %= MOD;    }    if up != 2 && left != 2 {        ans += process(i, j + 1, (s ^ (up << (j << 1))) | (2 << (j << 1)), n, m, dp);        ans %= MOD;    }    if up != 3 && left != 3 {        ans += process(i, j + 1, (s ^ (up << (j << 1))) | (3 << (j << 1)), n, m, dp);        ans %= MOD;    }    dp[i as usize][j as usize][s as usize] = ans;    return ans;}