Bomb Enemy

row和col的缓存只会在（上/左）就是“W”时需要更新

因此初始化或者（上/左）是墙的时候，可以计算一个临时的结果，在遇到另一个'W'时停止

这个缓存在遇到新一个“上/左”是墙的鸽子之前，都是有效的，无需重复计算

考虑到循环row, col的顺序，我们的row只用cache一个变量，col需要cache一个数组

public class Solution {
    public int maxKilledEnemies(char[][] grid) {
        if (grid == null || grid.length == 0 || grid[0] == null || grid[0].length == 0) {
            return 0;
        }
        int m = grid.length, n = grid[0].length;

        int rowHits = 0, colHits[] = new int[n];
        int max = 0;
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (j == 0 || grid[i][j - 1] == 'W') {
                    rowHits = 0;
                    for (int k = j; k < n && grid[i][k] != 'W'; k++) {
                        rowHits += grid[i][k] == 'E' ? 1 : 0;
                    }
                }
                if (i == 0 || grid[i - 1][j] == 'W') {
                    colHits[j] = 0;
                    for (int k = i; k < m && grid[k][j] != 'W'; k++) {
                        colHits[j] += grid[k][j] == 'E' ? 1 : 0;
                    }
                }

                if (grid[i][j] == '0') {
                    max = Math.max(max, rowHits + colHits[j]);
                }
            }
        }
        return max;
    }
}