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var surfaceArea = function (grid) {
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  let cube = 0,
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    overlap = 0;
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  for (let i = 0; i < grid.length; i++) {
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    for (let j = 0; j < grid[i].length; j++) {
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      cube += grid[i][j];
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      if (i > 0) {
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        overlap += Math.min(grid[i][j], grid[i - 1][j]);
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      } // x-direction
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      if (j > 0) {
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        overlap += Math.min(grid[i][j], grid[i][j - 1]);
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      } // y-direction
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      if (grid[i][j] > 1) {
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        overlap += grid[i][j] - 1;
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      } // z-direction
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    }
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  }
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  return cube * 6 - overlap * 2;
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};