361. Bomb Enemy

Given a 2D grid, each cell is either a wall 'W', an enemy 'E' or empty '0' (the number zero), return the maximum enemies you can kill using one bomb.
The bomb kills all the enemies in the same row and column from the planted point until it hits the wall since the wall is too strong to be destroyed.
Note: You can only put the bomb at an empty cell.

Example:

Input: [["0","E","0","0"],["E","0","W","E"],["0","E","0","0"]]
Output: 3 
Explanation: For the given grid,

0 E 0 0 
E 0 W E 
0 E 0 0

Placing a bomb at (1,1) kills 3 enemies.

Rust Solution

struct Solution;

impl Solution {
    fn max_killed_enemies(grid: Vec<Vec<char>>) -> i32 {
        let n = grid.len();
        if n == 0 {
            return 0;
        }
        let m = grid[0].len();
        let mut left = vec![vec![0; m]; n];
        let mut top = vec![vec![0; m]; n];
        let mut bottom = vec![vec![0; m]; n];
        let mut right = vec![vec![0; m]; n];
        for i in 0..n {
            for j in 0..m {
                match grid[i][j] {
                    'E' => {
                        top[i][j] = if i > 0 { top[i - 1][j] } else { 0 } + 1;
                        left[i][j] = if j > 0 { left[i][j - 1] } else { 0 } + 1;
                    }
                    'W' => {
                        top[i][j] = 0;
                        left[i][j] = 0;
                    }
                    _ => {
                        top[i][j] = if i > 0 { top[i - 1][j] } else { 0 };
                        left[i][j] = if j > 0 { left[i][j - 1] } else { 0 };
                    }
                }
            }
        }
        for i in (0..n).rev() {
            for j in (0..m).rev() {
                match grid[i][j] {
                    'E' => {
                        bottom[i][j] = if i + 1 < n { bottom[i + 1][j] } else { 0 } + 1;
                        right[i][j] = if j + 1 < m { right[i][j + 1] } else { 0 } + 1;
                    }
                    'W' => {
                        bottom[i][j] = 0;
                        right[i][j] = 0;
                    }
                    _ => {
                        bottom[i][j] = if i + 1 < n { bottom[i + 1][j] } else { 0 };
                        right[i][j] = if j + 1 < m { right[i][j + 1] } else { 0 };
                    }
                }
            }
        }
        let mut res = 0;
        for i in 0..n {
            for j in 0..m {
                if grid[i][j] == '0' {
                    res = res.max(top[i][j] + left[i][j] + bottom[i][j] + right[i][j]);
                }
            }
        }
        res
    }
}

#[test]
fn test() {
    let grid = vec_vec_char![
        ['0', 'E', '0', '0'],
        ['E', '0', 'W', 'E'],
        ['0', 'E', '0', '0']
    ];
    let res = 3;
    assert_eq!(Solution::max_killed_enemies(grid), res);
}

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