这两道题都需要建立row_vector and col_vector, 来统计每一行和每一列的信息。

Leetcode 807：
https://leetcode.com/problems/max-increase-to-keep-city-skyline/description/

class Solution {
public:
    int maxIncreaseKeepingSkyline(vector<vector<int>>& grid) {
        if(grid.empty() || grid[0].empty()){
            return 0;
        }
        
        int n = grid.size();
        vector<int> row_record(n, 0), col_record(n, 0);
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++){
                row_record[i] = max(row_record[i], grid[i][j]);
                col_record[j] = max(col_record[j], grid[i][j]);
            }
        }
        
        int total_sum = 0;
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++){
               total_sum += min(row_record[i], col_record[j]) - grid[i][j]; 
            }
        }
        
        return total_sum;
    }
};

Leetcode 531:
https://leetcode.com/problems/lonely-pixel-i/description/

class Solution {
public:
    int findLonelyPixel(vector<vector<char>>& picture) {
        if(picture.empty() || picture[0].empty()){
            return 0;
        }
        
        int row = picture.size(), col = picture[0].size();
        vector<int> row_record(row, 0);
        vector<int> col_record(col, 0);
        
        for(int i=0; i<row; i++){
            for(int j=0; j<col; j++){
                if(picture[i][j] == 'B'){
                    row_record[i]++;
                    col_record[j]++;
                }
            }
        }
        
        int cnt = 0;
        for(int i=0; i<row; i++){
            for(int j=0; j<col; j++){
                if(picture[i][j] == 'B'){
                    if(row_record[i] == 1 && col_record[j] == 1){
                        cnt++;
                    }
                }
            }
        }
        
        return cnt;
        
    }
};