STL algorithm find_end_algorithm find—

Find last subsequence in range

Searches the range [first1,last1) for the last occurrence of the sequence defined by [first2,last2), and returns an iterator to its first element.

The sequence of elements in [first2,last2) is compared to the possible subsequences of successive elements within [first1,last1) by either applying the == comparison operator to each element, or the template parameter comp (for the second version).

The behavior of this function template is equivalent to:

template<class ForwardIterator1, class ForwardIterator2>
  ForwardIterator1 find_end ( ForwardIterator1 first1, ForwardIterator1 last1,
                              ForwardIterator2 first2, ForwardIterator2 last2)
{
  ForwardIterator1 it1, limit, ret;
  ForwardIterator2 it2;

  limit=first1; advance(limit,1+distance(first1,last1)-distance(first2,last2));
  ret=last1;

  while (first1!=limit)
  {
    it1 = first1; it2 = first2;
    while (*it1==*it2)          // or: while (pred(*it1,*it2)) for the pred version
      { ++it1; ++it2; if (it2==last2) {ret=first1;break;} }
    ++first1;
  }
  return ret;
}

A similar algorithm function, but returning the first occurrence instead of the last, is search.

Parameters

first1, last1

Forward iterators to the initial and final positions of the searched sequence. The range used is [first1,last1), which contains all the elements between first1 and last1, including the element pointed by first1 but not the element pointed by last1.

first2, last2

Forward iterators to the initial and final positions of the sequence to be searched for. The range used is [first2,last2).

pred

Binary predicate taking two elements as argument (one of each of the two sequences), and returning the result of the comparison between them, with true (non-zero) meaning that they are to be considered equal, and false (zero) that they are not-equal. This can either be a pointer to a function or an object whose class overloads operator().

Return value

An iterator to the first element of the last occurrence of the sequence [first2,last2) in [first1,last1).
If the sequence is not found, the function returns last1.

Example

// find_end example
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

bool myfunction (int i, int j) {
  return (i==j);
}

int main () {
  int myints[] = {1,2,3,4,5,1,2,3,4,5};
  vector<int> myvector (myints,myints+10);
  vector<int>::iterator it;

  int match1[] = {1,2,3};

  // using default comparison:
  it = find_end (myvector.begin(), myvector.end(), match1, match1+3);

  if (it!=myvector.end())
    cout << "match1 last found at position " << int(it-myvector.begin()) << endl;

  int match2[] = {4,5,1};

  // using predicate comparison:
  it = find_end (myvector.begin(), myvector.end(), match2, match2+3, myfunction);

  if (it!=myvector.end())
    cout << "match2 last found at position " << int(it-myvector.begin()) << endl;
  
  return 0;
}

Output:

Match found at position 5
Match found at position 3

Complexity

At most, performs count2*(1+count1-count2) comparisons or applications of pred (where countX is the distance between firstX and lastX).