这个find_by_order()是一个内置的函数有序集这是一个基于策略的数据结构在C++中。基于策略的数据结构不属于C++标准模板库但的g ++编译器支持它们。
有序集是g ++中基于策略的数据结构,可以按排序的顺序维护唯一的元素。它以O(logN)复杂度执行STL中Set所执行的所有操作。除此之外,还以O(logN)复杂度执行以下两个操作:
- order_of_key (K): Number of items strictly smaller than K.
- find_by_order(k): Kth element in a Set (counting from zero).
find_by_order()函数接受一个称为K的键作为参数,并将迭代器返回给Kth集合中最大的元素。
例子:
Considering a Set S = {1, 5, 6, 17, 88},
s.find_by_order(0):Returns the 0th largest element, i.e. the minimum element, i.e. 1.
s.find_by_order(2):Returns the 2nd largest element, i.e. 6.Note: If K >= N, where N is the size of the set, then the function returns either 0 or in some compilers, the iterator to the smallest element.
下面是C++中find_by_order()函数的实现:
C++ 14
// C++ program to implement find_by_order()
// for Policy Based Data Structures
#include <bits/stdc++.h>
// Importing header files
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
// Declaring Ordered Set
typedef tree<int, null_type, less<int>, rb_tree_tag,
tree_order_statistics_node_update>
pbds;
// Driver Code
int main()
{
int arr[] = {1, 5, 6, 17, 88};
int n = sizeof(arr)/sizeof(arr[0]);
pbds S;
// Traverse the array
for (int i = 0; i < n; i++) {
// Insert array elements
// into the ordered set
S.insert(arr[i]);
}
// Returns iterator to 0-th
// largest element in the set
cout << *S.find_by_order(0) << " ";
// Returns iterator to 2-nd
// largest element in the set
cout << *S.find_by_order(2);
return 0;
}
输出:
1 6
注:本文由纯净天空筛选整理自p1173mayank大神的英文原创作品 find_by_order() in C++。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。