std:: lower_bound std:: upper_bound
std:: lower_bound
该函数返回范围内第一个不小于(大于或等于)指定val的值。如果序列中的值都小于val,则返回last.序列应该已经有序!
eg:
#include <iostream> #include <vector> #include <algorithm> using namespace std; int main(int argv,char **argc) { vector<int> v1{1,2,3,4}; cout<<"v1="; for(int i:v1) cout<<i<<" "; cout<<endl; auto it=lower_bound(v1.begin(),v1.end(),3); cout<<"lower_bound(v1.begin(),v1.end(),3)="<<*it<<endl; auto it2=lower_bound(v1.begin(),v1.end(),5); if(it2==v1.end()) cout<<"lower_bound(v1.begin(),v1.end(),5)=v1.end()"<<endl; else cout<<"lower_bound(v1.begin(),v1.end(),5)="<<*it2<<endl; }
截图:
std:: upper_bound
该函数返回范围内第一个 大于 指定val的值。如果序列中的值都小于val,则返回last.序列应该已经有序!
eg:
#include <iostream> // std::cout #include <algorithm> // std::lower_bound, std::upper_bound, std::sort #include <vector> // std::vector int main () { int myints[] = {10,20,30,30,20,10,10,20}; std::vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20 std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30 std::vector<int>::iterator low,up; low=std::lower_bound (v.begin(), v.end(), 20); // ^ up= std::upper_bound (v.begin(), v.end(), 20); // ^ std::cout << "lower_bound at position " << (low- v.begin()) << '\n'; std::cout << "upper_bound at position " << (up - v.begin()) << '\n'; return 0; }
截图:
另外,在map里的使用方法:
// map::lower_bound/upper_bound #include <iostream> #include <map> int main () { std::map<char,int> mymap; std::map<char,int>::iterator itlow,itup; mymap['a']=20; mymap['b']=40; mymap['c']=60; mymap['d']=80; mymap['e']=100; itlow=mymap.lower_bound ('b'); // itlow points to b itup=mymap.upper_bound ('d'); // itup points to e (not d!) mymap.erase(itlow,itup); // erases [itlow,itup) // print content: for (std::map<char,int>::iterator it=mymap.begin(); it!=mymap.end(); ++it) std::cout << it->first << " => " << it->second << '\n'; return 0; }
结果:
a => 20 e => 100