Leecode 892. 三维形体的表面积

class Solution {
    public int surfaceArea(int[][] grid) {
        int result = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                result += getFaceNum(grid, i, j);
            }
        }
        return result;
    }
    private int getFaceNum(int[][] grid, int i, int j) {
        if (grid[i][j] == 0){
            return 0;
        }
        int faceNum = grid[i][j] * 4 + 2;
        if (i - 1 >= 0) {
            faceNum -= Math.min(grid[i][j], grid[i - 1][j]);
        }
        if (j - 1 >= 0) {
            faceNum -= Math.min(grid[i][j], grid[i][j - 1]);
        }
        if (i + 1 < grid.length) {
            faceNum -= Math.min(grid[i][j], grid[i + 1][j]);
        }
        if (j + 1 < grid[0].length) {
            faceNum -= Math.min(grid[i][j], grid[i][j + 1]);
        }
        return faceNum;
    }
}