function shellSort(arr) {

var len = arr.length;

var gapSize = Math.floor(len / 2);

while (gapSize > 0) {

for (var i = gapSize; i < len; i++) {

var temp = arr[i];

var j = i;

while (j >= gapSize && arr[j - gapSize] > temp) {

arr[j] = arr[j - gapSize];

j -= gapSize;

}

arr[j] = temp;

}

gapSize = Math.floor(gapSize / 2);

}

return arr;

}

let arr = [6, 3, 2, 1, 5];

console.log(shellSort(arr));