function swap(arr, i, j){ 
var tmp = arr[i]; 
arr[i] = arr[j]; 
arr[j] = tmp; 
} 
function defaultCompare(a, b){ 
return a < b? -1: a > b? 1: 0; 
} 
var QuickSelect = function (arr, k, left, right, compare){ 
if (left === undefined) { 
left = 0; 
} 
if (right === undefined) { 
right = _AN_Read_length('length', arr) - 1; 
} 
if (compare === undefined) { 
compare = defaultCompare; 
} 
while (right > left){ 
if (right - left > 600) { 
var n = right - left + 1; 
var m = k - left + 1; 
var z = Math.log(n); 
var s = 0.5 * Math.exp(2 * z / 3); 
var sd = 0.5 * Math.sqrt(z * s * (n - s) / n) * (m - n / 2 < 0? -1: 1); 
var newLeft = Math.max(left, Math.floor(k - m * s / n + sd)); 
var newRight = Math.min(right, Math.floor(k + (n - m) * s / n + sd)); 
QuickSelect(arr, k, newLeft, newRight, compare); 
} 
var t = arr[k]; 
var i = left; 
var j = right; 
swap(arr, left, k); 
if (compare(arr[right], t) > 0) { 
swap(arr, left, right); 
} 
while (i < j){ 
swap(arr, i, j); 
i++ ; 
j-- ; 
while (compare(arr[i], t) < 0){ 
i++ ; 
} 
while (compare(arr[j], t) > 0){ 
j-- ; 
} 
} 
if (compare(arr[left], t) === 0) { 
swap(arr, left, j); 
} 
 else { 
j++ ; 
swap(arr, j, right); 
} 
if (j <= k) { 
left = j + 1; 
} 
if (k <= j) { 
right = j - 1; 
} 
} 
} 
; 
module.exports = QuickSelect;