C ++ STL set :: lower_bound()函数 (C++ STL set::lower_bound() function)

set::lower_bound() function is a predefined function, it is used to get the lower bound of any element in a set.

set :: lower_bound()函数是预定义的函数，用于获取集合中任何元素的下限。

it finds lower bound of any desired element from the set. Lower bound of any_element means the first number in the set that's not considered to go before any_element. So, if any_element is itself present, then it's any_element else immediate next of any_element.

它从集合中找到任何所需元素的下限。 any_element的下限是指集合中第一个不被认为在any_element之前的数字 。 因此，如果any_element本身存在，则它是any_element的下一个any_element 。

Prototype:

原型：

    set<T> st; //declaration
st<T> st::iterator it; //iterator declaration
it=st.upper_bound(T key);

Parameter: T key; //T is the data type

参数： T键； // T是数据类型

Return type: If lower_bound of the key exists in the set, Iterator pointer to the lower bound, Else, st.end()

返回类型：如果键的lower_bound存在于集合中，则迭代器指针指向下限，否则为st.end()

Usage:

用法：

The function finds lower bound of any desired element from the set. Lower bound of x means the first number in the set that's not considered to go before x. So, if x is itself present, then it's x else immediate next of x.

该函数从集合中找到任何所需元素的下限。 x的下限表示不考虑在x之前出现的集合中的第一个数字。 因此，如果x本身存在，则x紧接x 。

Example:

例：

    For a set of integer,
set<int> st;
st.insert(6);
st.insert(4);
st.insert(10);
set content: //sorted always(ordered)
4
6
10
it=st.lower_bound(6)
Print *it; //6
it=st.lower_bound(8)
Print *it; //10

Header file to be included:

包含的头文件：

    #include <iostream>
#include <set>
OR
#include <bits/stdc++.h>

C++ implementation:

C ++实现：

#include <bits/stdc++.h>
using namespace std;
void printSet(set<int> st){
set<int>:: iterator it;
cout<<"Set contents are:\n";
if(st.empty()){
cout<<"empty set\n";
return;
}
for(it=st.begin();it!=st.end();it++)
cout<<*it<<" ";
cout<<endl;
}
int main(){
cout<<"Example of lower_bound function\n";
set<int> st;
set<int>:: iterator it;
cout<<"inserting 4\n";
st.emplace(4);
cout<<"inserting 6\n";
st.emplace(6);
cout<<"inserting 10\n";
st.emplace(10);
printSet(st); //printing current set
cout<<"lower bound of 6 is "<<*(st.lower_bound(6));
return 0;
}

Output

输出量

Example of lower_bound function
inserting 4
inserting 6
inserting 10
Set contents are:
4 6 10
lower bound of 6 is 6

翻译自: https://www.includehelp.com/stl/set-lower_bound-function-in-cpp-stl.aspx