1591. Strange Printer II

There is a strange printer with the following two special requirements:

• On each turn, the printer will print a solid rectangular pattern of a single color on the grid. This will cover up the existing colors in the rectangle.
• Once the printer has used a color for the above operation, the same color cannot be used again.

You are given a m x n matrix targetGrid, where targetGrid[row][col] is the color in the position (row, col) of the grid.

Return true if it is possible to print the matrix targetGrid, otherwise, return false.

class Solution {
    bool isOnTop(vector<vector<int>>& grid, array<int,4>& range, int color) {
        int fr = range[0], fc = range[1], tr = range[2], tc = range[3];
        for(int i = fr; i <= tr; i++) {
            for(int j = fc; j <= tc; j++) {
                if(grid[i][j] == color or grid[i][j] == 0) continue;
                return false;
            }
        }
        
        for(int i = fr; i <= tr; i++) {
            for(int j = fc; j <= tc; j++) {
                grid[i][j] = 0;
            }
        }
        
        return true;
    }
public:
    bool isPrintable(vector<vector<int>>& targetGrid) {
        unordered_map<int, array<int,4>> colorRange;
        int n = targetGrid.size(), m = targetGrid[0].size();
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < m; j++) {
                int color = targetGrid[i][j];
                if(colorRange.count(color)) {
                    colorRange[color][1] = min(colorRange[color][1], j);
                    colorRange[color][3] = max(colorRange[color][3], j);
                    
                    colorRange[color][2] = i;
                } else {
                    colorRange[color] = {i,j,i,j};
                }
            }
        }
        while(!colorRange.empty()) {
            unordered_set<int> top;
            for(auto [color, range]: colorRange) {
                if(isOnTop(targetGrid, range, color)) {
                    top.insert(color);
                }
            }
            if(top.empty()) return false;
            for(auto tp : top) {
                colorRange.erase(tp);
            }
            
        }
        return true;
    }
};