老师您好，我在leetcode中的写法是这样的，运行超时，但始终不知道问题出在哪里，请问程序里面是哪里有问题

var getLeastNumbers = function(arr, k) {
    let len = arr.length
    if (!len || !k) return []
    let start = 0
    let end = len - 1
    let index = partition(arr, start, end)
    while(index !== k - 1) {
        if (index > k-1) {
            end = index-1
            index = partition(arr, start, end)
        } else {
            start = index + 1
            index = partition(arr, start, end)
        }
    }
    return arr.slice(0, k)
};

function partition(arr, left, right) {
    let pivot = arr[Math.floor(left+right)/2]
    while(left <=right) {
        while(arr[left]<pivot){
            left++
        }
        while(arr[right]>pivot){
            right--
        }
        if(left<=right){
            [arr[left],arr[right]]=[arr[right],arr[left]];
            left++;
            right--;
        }
    }
    return left;
}