classSolution{publicintsurfaceArea(int[][] grid){int n = grid.length, res =0;for(int i =0; i < n; i++){for(int j =0; j < n; j++){int level = grid[i][j];if(level >0){
res +=(level*4)+2;
res -= i >0? Math.min(level, grid[i-1][j])*2:0;
res -= j >0? Math.min(level, grid[i][j-1])*2:0;}}}return res;}}