随机快速排序详解-优快云博客

本文介绍了两种版本的随机快速排序算法实现，并对比了它们之间的主要区别。重点在于通过随机选取基准元素来改善传统快速排序中因初始数组部分有序而导致的性能下降问题。文中给出了详细的C++代码实现。

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两个版本的区别就在于swap

补充：随机快排

    int Partition(vector<int> &numbers, int st, int ed) {
        srand((unsigned)time(NULL));
        int pos = rand() % (ed-st+1) + st;
        swap(numbers[st], numbers[pos]);
        int tem = numbers[st];
        while(st < ed) {
            while(st < ed && tem <= numbers[ed]) ed--;
            numbers[st] = numbers[ed];
            while(st < ed && tem >= numbers[st]) st++;
            numbers[ed] = numbers[st];
        }
        numbers[st] = tem;
        return st;
    }

版本一

int partition(int arr[], int left, int right){
	int tem = arr[left];
	while(left < right){
		while(left < right && tem <= arr[right]) right--;
		arr[left] = arr[right];
		while(left < right && tem >= arr[left]) left++;
		arr[right] = arr[left];
	}
	arr[left] = tem;
	return left;

}
void sort(int arr[], int left, int right){
	if(left < right){
		int pos = partition(arr, left, right);
		sort(arr, left, pos-1);
		sort(arr, pos+1, right);
	}
}

版本二

int partition(int arr[], int left, int right){
	int tem = arr[left], i = left, j = right;
	while(i < j){
		while(i < j && tem <= arr[j]) j--;
		while(i < j && tem >= arr[i]) i++;
		if(i < j){
			int ttem = arr[i];
			arr[i] = arr[j];
			arr[j] = ttem;
		}
	}
	arr[left] = arr[i];
	arr[i] = tem;
	return i;

}
void sort(int arr[], int left, int right){
	if(left < right){
		int pos = partition(arr, left, right);
		sort(arr, left, pos-1);
		sort(arr, pos+1, right);
	}
}