Matrix Diagonal Sum LeetCode solution in C++

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class Solution {
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 public:
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  int diagonalSum(vector<vector<int>> &mat) {
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    int n = mat.size();
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    int ans = 0;
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    for (int i = 0; i < n; i++) {
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      ans = ans + mat[i][i] + mat[i][n - i - 1];
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    }
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    ans = (n & 1) ? ans - mat[n / 2][n / 2]
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                  : ans; // if n is odd then we have to subtract mat[n/2][n/2]
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                         // from the ans because we add it twice earlier.
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    return ans;
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  }
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};