Flip Columns For Maximum Number of Equal Rows LeetCode solution in JavaScript

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var maxEqualRowsAfterFlips = function (matrix) {
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  const m = matrix.length;
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  const n = matrix[0].length;
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  const map = new Map();
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  let max = 0;
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  for (let i = 0; i < m; i++) {
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    let normal = 0;
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    let reversed = 0;
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    for (let j = 0; j < n; j++) {
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      normal = (normal << 1) | matrix[i][j];
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      reversed = (reversed << 1) | (1 - matrix[i][j]);
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    }
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    if (!map.has(normal)) map.set(normal, 0);
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    map.set(normal, map.get(normal) + 1);
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    max = Math.max(max, map.get(normal));
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    if (!map.has(reversed)) map.set(reversed, 0);
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    map.set(reversed, map.get(reversed) + 1);
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    max = Math.max(max, map.get(reversed));
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  }
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  return max;
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};