STL Source Code Anatomy algorithm Stl_algo.h--Equal_range

This article is Senlie original, reprint please retain this address:Http://blog.csdn.net/zhengsenlie

Equal_range (applied to ordered interval)

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Descriptive narration: Using binary search to find an interval, all values in the interval are equal to the given value, and a pair is returned.
Upper bound iterators and nether iterators for each storage interval

Source:

Template <class ForwardIterator, class T>inline Pair<forwarditerator, Forwarditerator>equal_range ( ForwardIterator first, ForwardIterator last, const t& value) {return __equal_range (first, last, value, Distance_type (first), Iterator_category (first));} ForwardIterator version number template <class ForwardIterator, class T, class Distance>pair<forwarditerator, Forwarditerator>__equal_range (ForwardIterator First, ForwardIterator last, const t& value, distance*,  Forward_iterator_tag) {Distance len = 0;  Distance (first, last, Len);  Distance half;  ForwardIterator middle, left, right; while (Len > 0) {//strange? Why not just use Lower_bound, upper_bound, but wait to find the value to use again? And I think it's about efficiency.
Find value first, then the left and right two intervals may have shrunk a lot.    Re-using Lower_bound and upper_bound cost a lot less half = Len >> 1;    middle = first;    Advance (middle, half);      if (*middle < value) {first = middle;      ++first;    len = len-half-1;    } else if (value < *middle) len = half;      else {left = Lower_bound (first, middle, value);      Advance (first, Len);      right = Upper_bound (++middle, first, value);    Return Pair<forwarditerator, forwarditerator> (left, right); }} return Pair<forwarditerator, Forwarditerator> (first, first);} Randomaccessiterator version number template <class Randomaccessiterator, class T, class distance>pair<              Randomaccessiterator, Randomaccessiterator>__equal_range (randomaccessiterator First, RandomAccessIterator last,  Const t& value, distance*, Random_access_iterator_tag) {Distance len = Last-first;  Distance half;  Randomaccessiterator Middle, left, right;    while (Len > 0) {half = Len >> 1; Middle = First + half;      if (*middle < value) {first = middle + 1;    len = len-half-1;    } else if (value < *middle) len = half;      else {left = Lower_bound (first, middle, value);      right = Upper_bound (++middle, first + len, value);                                                              Return Pair<randomaccessiterator, randomaccessiterator> (left,    right); }} return Pair<randomaccessiterator, Randomaccessiterator> (first, first);}

Demo Sample:

int main () {  int a[] = {1, 2, 3, 3, 3, 5, 8};  const int N = sizeof (A)/sizeof (int);  for (int i = 2; I <= 4; ++i) {    pair<int*, int*> result = Equal_range (A, a + N, i);    cout << Endl;    cout << "Searching for" << i << Endl;    cout << "first  position where" << I << "could be inserted:"         << result.first-a <&L T Endl;    cout << "Last  position where" << I << "could be inserted:"         << result.second-a < < Endl;    if (Result.first < A + N)      cout << "  *result.first =" << *result.first << Endl;    if (Result.second < A + N)      cout << "  *result.second =" << *result.second << Endl;  }}

/* The  output is:searching for 2 first  position where 2 could is inserted:1 last  position where 2 could is in Serted:2  *result.first = 2  *result.second = 3Searching for 3 first  position where 3 could is inserted:2  Last position where 3 could is inserted:5  *result.first = 3  *result.second = 5Searching for 4 first  position Where 4 could is inserted:5 last  position where 4 could be inserted:5  *result.first = 5  *result.second = 5*/

STL Source Code Anatomy algorithm Stl_algo.h--Equal_range