mirror of
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250 lines
7.3 KiB
C++
250 lines
7.3 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_BinarySearch_h
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#define mozilla_BinarySearch_h
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#include "mozilla/Assertions.h"
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#include "mozilla/CompactPair.h"
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#include <stddef.h>
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namespace mozilla {
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/*
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* The BinarySearch() algorithm searches the given container |aContainer| over
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* the sorted index range [aBegin, aEnd) for an index |i| where
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* |aContainer[i] == aTarget|.
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* If such an index |i| is found, BinarySearch returns |true| and the index is
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* returned via the outparam |aMatchOrInsertionPoint|. If no index is found,
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* BinarySearch returns |false| and the outparam returns the first index in
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* [aBegin, aEnd] where |aTarget| can be inserted to maintain sorted order.
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*
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* Example:
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*
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* Vector<int> sortedInts = ...
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*
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* size_t match;
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* if (BinarySearch(sortedInts, 0, sortedInts.length(), 13, &match)) {
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* printf("found 13 at %lu\n", match);
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* }
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*
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* The BinarySearchIf() version behaves similarly, but takes |aComparator|, a
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* functor to compare the values with, instead of a value to find.
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* That functor should take one argument - the value to compare - and return an
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* |int| with the comparison result:
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*
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* * 0, if the argument is equal to,
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* * less than 0, if the argument is greater than,
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* * greater than 0, if the argument is less than
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*
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* the value.
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*
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* Example:
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*
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* struct Comparator {
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* int operator()(int aVal) const {
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* if (mTarget < aVal) { return -1; }
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* if (mTarget > aVal) { return 1; }
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* return 0;
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* }
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* explicit Comparator(int aTarget) : mTarget(aTarget) {}
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* const int mTarget;
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* };
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*
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* Vector<int> sortedInts = ...
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*
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* size_t match;
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* if (BinarySearchIf(sortedInts, 0, sortedInts.length(), Comparator(13),
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* &match)) { printf("found 13 at %lu\n", match);
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* }
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*
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*/
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template <typename Container, typename Comparator>
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bool BinarySearchIf(const Container& aContainer, size_t aBegin, size_t aEnd,
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const Comparator& aCompare,
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size_t* aMatchOrInsertionPoint) {
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MOZ_ASSERT(aBegin <= aEnd);
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size_t low = aBegin;
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size_t high = aEnd;
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while (high != low) {
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size_t middle = low + (high - low) / 2;
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// Allow any intermediate type so long as it provides a suitable ordering
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// relation.
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const int result = aCompare(aContainer[middle]);
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if (result == 0) {
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*aMatchOrInsertionPoint = middle;
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return true;
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}
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if (result < 0) {
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high = middle;
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} else {
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low = middle + 1;
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}
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}
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*aMatchOrInsertionPoint = low;
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return false;
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}
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namespace detail {
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template <class T>
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class BinarySearchDefaultComparator {
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public:
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explicit BinarySearchDefaultComparator(const T& aTarget) : mTarget(aTarget) {}
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template <class U>
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int operator()(const U& aVal) const {
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if (mTarget == aVal) {
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return 0;
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}
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if (mTarget < aVal) {
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return -1;
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}
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return 1;
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}
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private:
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const T& mTarget;
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};
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} // namespace detail
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template <typename Container, typename T>
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bool BinarySearch(const Container& aContainer, size_t aBegin, size_t aEnd,
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T aTarget, size_t* aMatchOrInsertionPoint) {
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return BinarySearchIf(aContainer, aBegin, aEnd,
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detail::BinarySearchDefaultComparator<T>(aTarget),
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aMatchOrInsertionPoint);
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}
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/*
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* LowerBound(), UpperBound(), and EqualRange() are equivalent to
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* std::lower_bound(), std::upper_bound(), and std::equal_range() respectively.
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*
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* LowerBound() returns an index pointing to the first element in the range
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* in which each element is considered *not less than* the given value passed
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* via |aCompare|, or the length of |aContainer| if no such element is found.
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*
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* UpperBound() returns an index pointing to the first element in the range
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* in which each element is considered *greater than* the given value passed
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* via |aCompare|, or the length of |aContainer| if no such element is found.
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*
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* EqualRange() returns a range [first, second) containing all elements are
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* considered equivalent to the given value via |aCompare|. If you need
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* either the first or last index of the range, LowerBound() or UpperBound(),
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* which is slightly faster than EqualRange(), should suffice.
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*
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* Example (another example is given in TestBinarySearch.cpp):
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*
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* Vector<const char*> sortedStrings = ...
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*
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* struct Comparator {
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* const nsACString& mStr;
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* explicit Comparator(const nsACString& aStr) : mStr(aStr) {}
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* int32_t operator()(const char* aVal) const {
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* return mStr.Compare(aVal);
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* }
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* };
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*
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* auto bounds = EqualRange(sortedStrings, 0, sortedStrings.length(),
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* Comparator("needle I'm looking for"_ns));
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* printf("Found the range [%zd %zd)\n", bounds.first(), bounds.second());
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*
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*/
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template <typename Container, typename Comparator>
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size_t LowerBound(const Container& aContainer, size_t aBegin, size_t aEnd,
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const Comparator& aCompare) {
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MOZ_ASSERT(aBegin <= aEnd);
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size_t low = aBegin;
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size_t high = aEnd;
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while (high != low) {
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size_t middle = low + (high - low) / 2;
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// Allow any intermediate type so long as it provides a suitable ordering
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// relation.
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const int result = aCompare(aContainer[middle]);
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// The range returning from LowerBound does include elements
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// equivalent to the given value i.e. aCompare(element) == 0
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if (result <= 0) {
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high = middle;
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} else {
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low = middle + 1;
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}
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}
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return low;
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}
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template <typename Container, typename Comparator>
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size_t UpperBound(const Container& aContainer, size_t aBegin, size_t aEnd,
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const Comparator& aCompare) {
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MOZ_ASSERT(aBegin <= aEnd);
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size_t low = aBegin;
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size_t high = aEnd;
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while (high != low) {
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size_t middle = low + (high - low) / 2;
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// Allow any intermediate type so long as it provides a suitable ordering
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// relation.
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const int result = aCompare(aContainer[middle]);
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// The range returning from UpperBound does NOT include elements
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// equivalent to the given value i.e. aCompare(element) == 0
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if (result < 0) {
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high = middle;
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} else {
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low = middle + 1;
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}
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}
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return high;
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}
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template <typename Container, typename Comparator>
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CompactPair<size_t, size_t> EqualRange(const Container& aContainer,
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size_t aBegin, size_t aEnd,
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const Comparator& aCompare) {
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MOZ_ASSERT(aBegin <= aEnd);
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size_t low = aBegin;
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size_t high = aEnd;
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while (high != low) {
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size_t middle = low + (high - low) / 2;
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// Allow any intermediate type so long as it provides a suitable ordering
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// relation.
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const int result = aCompare(aContainer[middle]);
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if (result < 0) {
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high = middle;
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} else if (result > 0) {
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low = middle + 1;
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} else {
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return MakeCompactPair(
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LowerBound(aContainer, low, middle, aCompare),
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UpperBound(aContainer, middle + 1, high, aCompare));
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}
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}
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return MakeCompactPair(low, high);
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}
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} // namespace mozilla
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#endif // mozilla_BinarySearch_h
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