Magic Squares In Grid LeetCode solution in C++

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class Solution {
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 public:
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  int numMagicSquaresInside(vector<vector<int>> &grid) {
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    int result = 0;
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    for (int i = 0; i < grid.size(); i++) {
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      for (int j = 0; j < grid[i].size(); j++) {
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        if (isMagicSquare(grid, i, j)) {
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          result++;
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        }
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      }
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    }
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    return result;
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  }
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  bool isMagicSquare(vector<vector<int>> &grid, int i, int j) {
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    if (i + 2 < grid.size() && j + 2 < grid[i].size()) {
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      int col1 = grid[i][j] + grid[i + 1][j] + grid[i + 2][j];
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      int col2 = grid[i][j + 1] + grid[i + 1][j + 1] + grid[i + 2][j + 1];
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      int col3 = grid[i][j + 2] + grid[i + 1][j + 2] + grid[i + 2][j + 2];
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      int row1 = grid[i][j] + grid[i][j + 1] + grid[i][j + 2];
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      int row2 = grid[i + 1][j] + grid[i + 1][j + 1] + grid[i + 1][j + 2];
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      int row3 = grid[i + 2][j] + grid[i + 2][j + 1] + grid[i + 2][j + 2];
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      int diag1 = grid[i][j] + grid[i + 1][j + 1] + grid[i + 2][j + 2];
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      int diag2 = grid[i + 2][j] + grid[i + 1][j + 1] + grid[i][j + 2];
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      if ((col1 == col2) && (col1 == col3) && (col1 == row1) && (col1 == row2) && (col1 == row3) &&
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          (col1 == diag1) && (col1 == diag2)) {
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        set<int> s({1, 2, 3, 4, 5, 6, 7, 8, 9});
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        for (int r = 0; r < 3; r++) {
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          for (int c = 0; c < 3; c++) {
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            s.erase(grid[i + r][j + c]);
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          }
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        }
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        return s.empty();
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      }
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    }
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    return false;
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  }
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};