upper_bound

Algorithm

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• Complexity
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Determines the last valid position for a value in a sorted container.

None

#include <algorithm>
template <class ForwardIterator, class T> 
  ForwardIterator
    upper_bound(ForwardIterator first, ForwardIterator last,
                const T& value);
template <class ForwardIterator, class T, class Compare>
  ForwardIterator
    upper_bound(ForwardIterator first, ForwardIterator last,
                const T& value, Compare comp);

The upper_bound algorithm is one of a set of binary search algorithms. All of these algorithms perform binary searches on ordered containers. Each algorithm has two versions. The first version uses the less than operator (operator<) to perform the comparison, and assumes that the sequence has been sorted using that operator. The second version allows you to include a function object of type Compare, and assumes that Compare is the function used to sort the sequence. The function object must be a binary predicate.

The upper_bound algorithm finds the last position in a container that value can occupy without violating the container's ordering. upper_bound's return value is the iterator for the first element in the container that is greater than value, or, when the comparison operator is used, the first element that does NOT satisfy the comparison function. Because the algorithm is restricted to using the less than operator or the user-defined function to perform the search, upper_bound returns an iterator i in the range [first, last) such that for any iterator j in the range [first, i) the appropriate version of the following conditions holds:

!(value < *j)

or

comp(value, *j) == false

upper_bound performs at most log(last - first) + 1 comparisons.

//
// ul_bound.cpp
//
#include <vector>
#include <algorithm>
#include <functional>
#include <iostream>
using namespace std;

int main()
 {
typedef vector<int>::iterator iterator;
int d1[11] = {0,1,2,2,3,4,2,2,2,6,7};

// Set up a vector
vector<int> v1(d1 + 0,d1 + 11);

// Try lower_bound variants
iterator it1 = lower_bound(v1.begin(),v1.end(),3);
// it1 = v1.begin() + 4

iterator it2 = 
   lower_bound(v1.begin(),v1.end(),2,less<int>());
// it2 = v1.begin() + 4

// Try upper_bound variants
iterator it3 = upper_bound(v1.begin(),v1.end(),3);
// it3 = vector + 5

iterator it4 = 
   upper_bound(v1.begin(),v1.end(),2,less<int>());
// it4 = v1.begin() + 5 
cout << endl << endl
     << "The upper and lower bounds of 3: ( "
     << *it1 << " , " << *it3 << " ]" << endl;
cout << endl << endl
     << "The upper and lower bounds of 2: ( "
     << *it2 << " , " << *it4 << " ]" << endl;
return 0;
 }

Program Output

The upper and lower bounds of 3: ( 3 , 4 ]
The upper and lower bounds of 2: ( 2 , 3 ]

If your compiler does not support default template parameters, then you always need to supply the Allocator template argument. For instance, you need to write:

vector<int, allocator<int> >

instead of:

vector<int>

If your compiler does not support namespaces, then you do not need the using declaration for std.

lower_bound, equal_range