Count Artifacts That Can Be Extracted LeetCode solution in C++

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class Solution {
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 public:
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  int digArtifacts(int n, vector<vector<int>> &artifacts, vector<vector<int>> &dig) {
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    vector<vector<int>> arr(n, vector<int>(n, 1));
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    for (vector<int> &v : dig) {
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      arr[v[0]][v[1]] = 0;
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    }
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    int preSum[n + 1][n + 1];
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    for (int i = 0; i <= n; i++) {
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      preSum[i][0] = 0;
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      preSum[0][i] = 0;
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    }
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    for (int i = 1; i <= n; i++) {
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      for (int j = 1; j <= n; j++) {
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        preSum[i][j] =
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            preSum[i - 1][j] + preSum[i][j - 1] - preSum[i - 1][j - 1] + arr[i - 1][j - 1];
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      }
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    }
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    int res = 0, sum, r1, c1, r2, c2;
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    for (vector<int> &v : artifacts) {
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      r1 = v[0];
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      c1 = v[1];
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      r2 = v[2];
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      c2 = v[3];
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      sum = preSum[r2 + 1][c2 + 1] - preSum[r1][c2 + 1] - preSum[r2 + 1][c1] + preSum[r1][c1];
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      if (sum == 0) {
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        res++;
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      }
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    }
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    return res;
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  }
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};