STL algorithm algorithms lower_bound and upper_bound (31)

Lower_bound prototype:

Function template <algorithm> STD: lower_bound

Default (1)	template <class ForwardIterator, class T> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val);
Custom (2)	template <class ForwardIterator, class T, class Compare> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp);

This function returns the first value not less than (greater than or equal to) specified Val in the range.

If the values in the sequence are smaller than Val, the return value is last.

The sequence should be ordered!

Use operator <to compare the sizes of the two elements.

This function optimizes the comparison times of non-continuous storage sequences.

The behavior is similar:

template <class ForwardIterator, class T>  ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val){  ForwardIterator it;  iterator_traits<ForwardIterator>::difference_type count, step;  count = distance(first,last);  while (count>0)  {    it = first; step=count/2; advance (it,step);    if (*it<val) {                 // or: if (comp(*it,val)), for version (2)      first=++it;      count-=step+1;    }    else count=step;  }  return first;}

A simple example:

#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;elsecout<<"lower_bound(v1.begin(),v1.end(),5)="<<*it2<<endl;}

Run:

Upper_bound prototype:

Function template <algorithm> STD: upper_bound

Default (1)	template <class ForwardIterator, class T> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val);
Custom (2)	template <class ForwardIterator, class T, class Compare> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp);

This function returns the first value in the range greater than the specified Val.

If the values in the sequence are smaller than Val, the return value is last.

The sequence should be ordered!

Use operator <to compare the sizes of the two elements.

This function optimizes the comparison times of non-continuous storage sequences.

The behavior is similar:

template <class ForwardIterator, class T>  ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val){  ForwardIterator it;  iterator_traits<ForwardIterator>::difference_type count, step;  count = std::distance(first,last);  while (count>0)  {    it = first; step=count/2; std::advance (it,step);    if (!(val<*it))                 // or: if (!comp(val,*it)), for version (2)      { first=++it; count-=step+1;  }    else count=step;  }  return first;}

A simple example:

// lower_bound/upper_bound example#include <iostream>     // std::cout#include <algorithm>    // std::lower_bound, std::upper_bound, std::sort#include <vector>       // std::vectorint 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;}

Running result:

The values returned by lower_bound and upper_bound are exactly the two values corresponding to interval _range!

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STL algorithm algorithms lower_bound and upper_bound (31)