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var pancakeSort = function (arr) {
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  let res = [];
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  for (let i = arr.length; i > 0; i--) {
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    //search the array for all values from 1 to n
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    let idx = arr.indexOf(i);
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    if (idx != i - 1) {
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      // if value is not present at its desired index
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      let pancake = arr.slice(0, idx + 1).reverse(); //flip the array with k=index of value i to put it in front of the array
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      res.push(idx + 1);
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      arr = arr.slice(idx + 1);
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      arr = pancake.concat(arr); //value i is now at index 0
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      pancake = arr.slice(0, i).reverse(); //flip the array with k = i-1 to put the value at its place
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      res.push(i);
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      arr = arr.slice(i);
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      arr = pancake.concat(arr); //now the array is sorted from i to n
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    }
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  }
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  return res;
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};