C++ set upper_bound()用法及代码示例

set::upper_bound()是C++ STL中的内置函数，该函数返回一个迭代器，该迭代器指向刚好大于k的下一个元素。如果参数中传递的 key 超过了容器中的最大 key ，则迭代器将返回指向设置容器中最后一个元素的下一个元素(可以使用set end()函数标识)。

用法:

set_name.upper_bound(key)

参数：此函数接受单个强制性参数键，该键指定要返回其上限的元素。

返回值：该函数返回一个迭代器，该迭代器指向刚好大于k的下一个元素。如果参数中传递的键超过了容器中的最大键，则迭代器指向std::end(，它指向集合中最后一个元素旁边的元素。

示例1:以下示例程序旨在说明上述函数：

// CPP program to demonstrate the 
// set::upper_bound() function 
#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    set<int> s; 
  
    // Function to insert elements 
    // in the set container 
    s.insert(1); 
    s.insert(4); 
    s.insert(2); 
    s.insert(5); 
    s.insert(6); 
  
    cout << "The set elements are: "; 
    for (auto it = s.begin(); it != s.end(); it++) 
        cout << *it << " "; 
  
    // when 2 is present 
    // points to next element after 2 
    auto it = s.upper_bound(2); 
    cout << "\nThe upper bound of key 2 is "; 
    cout << (*it) << endl; 
  
    // when 3 is not present 
    // points to next greater after 3 
    it = s.upper_bound(3); 
    cout << "The upper bound of key 3 is "; 
    cout << (*it) << endl; 
  
    return 0; 
}

输出：

The set elements are: 1 2 4 5 6 
The upper bound of key 2 is 4
The upper bound of key 3 is 4

示例2:下面是一个更好的代码，它还检查给定元素是否大于或等于最大元素。

// CPP program to demonstrate the 
// set::upper_bound() function 
#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    set<int> s; 
  
    // Function to insert elements 
    // in the set container 
    s.insert(1); 
    s.insert(4); 
    s.insert(2); 
    s.insert(5); 
    s.insert(6); 
  
    int key = 8; 
    auto it = s.upper_bound(key); 
    if (it == s.end()) 
        cout << "The given key is greater "
                "than or equal to the largest element \n"; 
    else
        cout << "The immediate greater element "
             << "is " << *it << endl; 
  
    key = 3; 
    it = s.upper_bound(key); 
    if (it == s.end()) 
        cout << "The given key is greater "
                "than or equal to the largest element \n"; 
    else
        cout << "The immediate greater element "
             << "is " << *it << endl; 
  
    return 0; 
}

输出：

The given key is greater than or equal to the largest element 
The immediate greater element is 4

相关用法

注：本文由纯净天空筛选整理自gopaldave大神的英文原创作品 set upper_bound() function in C++ STL。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。