1
var matrixReshape = function (mat, r, c) {
2
  const origR = mat.length;
3
  const origC = mat[0].length;
4

5
  if (r * c !== origR * origC) {
6
    return mat;
7
  }
8

9
  const flat = mat.flatMap((n) => n);
10

11
  const output = [];
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  for (let i = 0; i < flat.length; i++) {
13
    if (i % c === 0) {
14
      output.push([]);
15
    }
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    output[output.length - 1].push(flat[i]);
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  }
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  return output;
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};