912. Sort an Array

这道题就是考排序。

用快速排序，每次划分的时候随机选择一个数作为Pivot，不然会超时。

class Solution {
public:
    vector<int> sortArray(vector<int>& nums) {
        std::srand(static_cast<unsigned int>(std::time(nullptr)));
        quick_sort(nums,0,nums.size()-1);
        return nums;
    }

    void quick_sort(vector<int>& nums,int left,int right){
        if(left>=right)
            return;
        int pos = partition(nums,left,right);
        quick_sort(nums,left,pos-1);
        quick_sort(nums,pos+1,right);
    }
    int partition(vector<int>& nums,int left,int right)
    {
        if(left >= right)
            return left;
        int random_pos = left + std::rand() % (right - left + 1);
        std::swap(nums[left],nums[random_pos]);
        int pivot = nums[left];
        while(left<right){
            while(left<right && pivot <= nums[right]) right--;
            nums[left] = nums[right];
            while(left<right && pivot >= nums[left]) left++;
            nums[right] = nums[left];
        }
        nums[left] = pivot;
        return left;
    }
};