[C++知识库]ECNU 华东师范大学 OJ Problem #2572. Sort it…满分题解【快速排序】

单点时限:?2.0 sec

内存限制:?256 MB

There is a database,partychen want you to sort the database’s data in the order from the least up to the greatest element,then do the query: “Which element is i-th by its value?”- with i being a natural number in a range from 1 to N.

It should be able to process quickly queries like this.

输入格式

The standard input of the problem consists of two parts. At first, a database is written, and then there’s a sequence of queries. The format of database is very simple: in the first line there’s a number?N(1?N?100000), in the next N lines there are numbers of the database one in each line in an arbitrary order. A sequence of queries is written simply as well: in the first line of the sequence a number of queries?K(1?K?100)?is written, and in the next?K?lines there are queries one in each line. The query “Which element is i-th by its value?” is coded by the number i.

输出格式

The output should consist of K lines. In each line there should be an answer to the corresponding query. The answer to the query “i” is an element from the database, which is i-th by its value (in the order from the least up to the greatest element).

样例

input

5
7
121
123
7
121
3
3
2
5

output

121
7
123

提示

Hint
After we sort the data we get 7 7 121 121 123,so the postion 3 is 121,the postion 2 is 7 and the position 5 is 123 etc.

代码如下：

#include<iostream>
using namespace std;

int partition(int A[], int low, int high)
{
	int i = low, j = high + 1;
	int p = A[low];
	while (true) {
		while (A[++i] < p && i < high);//从左到右找大的
		while (A[--j] > p);//从右到左找小的
		if (i >= j)break;
		swap(A[i], A[j]);
	}
	A[low] = A[j];
	A[j] = p;
	return j;
}

void quickSort(int A[], int low, int high)
{
	if (low < high) {
		int j = partition(A, low, high);
		quickSort(A, low, j - 1);
		quickSort(A, j + 1, high);
	}
}

int main()
{
	int n;
	cin >> n;
	int A[100001];
	for (int i = 1; i <= n; i++)
		cin >> A[i];
	int queries;
	cin >> queries;
	int q[100];
	for (int i = 0; i < queries; i++)
		cin >> q[i];
	quickSort(A, 1, n);
	for (int i = 0; i < queries; i++)
		cout << A[q[i]] << endl;
	return 0;
}

运行结果如下：

?