分治-快速排序系列一＞快速排序

public int[] sortArray(int[] nums) {
        qsort(nums,0,nums.length-1);
        return nums;
    }

    private void qsort(int[] nums, int L, int r){
        if(L >= r) return;

        int key = nums[new Random().nextInt(r-L+1)+L];//基准元素
        int left = L-1,right = r+1,i = L;//注意这里的left和right会随递归改变，不能写死

        while(i < right){
            if(key > nums[i]) swap(nums, ++left, i++);
            else if(key == nums[i]) i++;
            else swap(nums, --right, i);
        }

        //[L,letf][letf+1,right-1][right,r]
        qsort(nums,L,left);
        qsort(nums,right,r);
    }

    private void swap(int[] nums, int i, int j){
        int t = nums[i];
        nums[i] = nums[j];
        nums[j] = t;
    }