출처 : https://leetcode.com/problems/projection-area-of-3d-shapes/
You are given an n x n grid where we place some 1 x 1 x 1 cubes that are axis-aligned with the x, y, and z axes.
Each value v = grid[i][j] represents a tower of v cubes placed on top of the cell (i, j).
We view the projection of these cubes onto the xy, yz, and zx planes.
A projection is like a shadow, that maps our 3-dimensional figure to a 2-dimensional plane. We are viewing the "shadow" when looking at the cubes from the top, the front, and the side.
Return the total area of all three projections.

class Solution {
public int projectionArea(int[][] grid) {
int x = 0, y = 0, z = 0;
for (int i = 0; i < grid.length; i++) {
int maxY = 0;
for (int j = 0; j < grid[i].length; j++) {
if (grid[i][j] != 0) x++;
if (maxY < grid[i][j]) maxY = grid[i][j];
}
y += maxY;
}
for (int q = 0; q < grid.length; q++) {
int maxZ = 0;
for (int p = 0; p < grid.length; p++) {
if (grid[p][q] > maxZ) maxZ = grid[p][q];
}
z += maxZ;
}
return x + y + z;
}
}