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72 lines
2.0 KiB
C++
72 lines
2.0 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 <stddef.h>
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namespace mozilla {
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/*
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* The algorithm searches the given container |aContainer| over the sorted
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* index range [aBegin, aEnd) for an index |i| where |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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template <typename Container, typename T>
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bool
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BinarySearch(const Container& aContainer, size_t aBegin, size_t aEnd,
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T aTarget, size_t* aMatchOrInsertionPoint)
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{
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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 (low != high) {
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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 auto& middleValue = aContainer[middle];
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MOZ_ASSERT(aContainer[low] <= aContainer[middle]);
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MOZ_ASSERT(aContainer[middle] <= aContainer[high - 1]);
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MOZ_ASSERT(aContainer[low] <= aContainer[high - 1]);
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if (aTarget == middleValue) {
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*aMatchOrInsertionPoint = middle;
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return true;
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}
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if (aTarget < middleValue) {
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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 mozilla
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#endif // mozilla_BinarySearch_h
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