LeetCode "Range Sum Query 2D - Immutable"

Yes the accu* is not necessary :)

class NumMatrix {
  vector<vector<int>> dp;
public:

    NumMatrix(vector<vector<int>> &matrix) {

        int h = matrix.size();
        if(!h) return;
    int w = matrix[0].size();
    
    vector<vector<int>> accuCols(h, vector<int>(w));
    vector<vector<int>> accuRows(h, vector<int>(w));
    
    // Accumulated Col sums
    for(int i = 0; i < w; i ++)
    {
      accuCols[0][i] = matrix[0][i];
      for(int j = 1; j < h; j ++)
      {
        accuCols[j][i] = accuCols[j - 1][i] + matrix[j][i];        
      }
    }
    
    // Accumulated Row sums
    for(int j = 0; j < h; j ++)
    {
      accuRows[j][0] = matrix[j][0];
      for(int i = 1; i < w; i ++)
      {
        accuRows[j][i] = accuRows[j][i - 1] + matrix[j][i];        
      }
    }
    
    dp.assign(h + 1, vector<int>(w + 1, 0));
    for(int i = 0; i < h; i ++)
    for(int j = 0; j < w; j ++)
    {
        dp[i + 1][j + 1] = dp[i][j] + accuCols[i][j] + accuRows[i][j] - matrix[i][j];   
    }
    }

    int sumRegion(int row1, int col1, int row2, int col2) 
    {    
    int v = dp[row2 + 1][col2 + 1] - dp[row1][col1];     
    int u = dp[row1][col2 + 1] - dp[row1][col1];
    int l = dp[row2 + 1][col1] - dp[row1][col1];
    return v - u - l;
    }
};