Matrix Diagonal Sum LeetCode solution in JavaScript

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var diagonalSum = function (mat) {
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  return mat.reduce((acc, matrix, i) => {
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    const matrixlength = matrix.length - 1;
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    return (acc +=
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      i !== matrixlength - i
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        ? matrix[i] + matrix[matrixlength - i]
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        : matrix[i]);
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  }, 0);
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};
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/*
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Runtime: 67 ms, faster than 92.84% of JavaScript online submissions for Matrix Diagonal Sum.
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Memory Usage: 42.9 MB, less than 88.29% of JavaScript online submissions for Matrix Diagonal Sum.
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*/