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67 lines
1.8 KiB
C++
67 lines
1.8 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 'c' over the sorted index range
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* [begin, end) for an index 'i' where 'c[i] == target'. If such an index 'i' is
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* found, BinarySearch returns 'true' and the index is returned via the outparam
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* 'matchOrInsertionPoint'. If no index is found, BinarySearch returns 'false'
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* and the outparam returns the first index in [begin, end] where 'target' can
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* 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 &c, size_t begin, size_t end, T target, size_t *matchOrInsertionPoint)
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{
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MOZ_ASSERT(begin <= end);
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size_t low = begin;
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size_t high = end;
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while (low != high) {
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size_t middle = low + (high - low) / 2;
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const T &middleValue = c[middle];
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MOZ_ASSERT(c[low] <= c[middle]);
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MOZ_ASSERT(c[middle] <= c[high - 1]);
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MOZ_ASSERT(c[low] <= c[high - 1]);
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if (target == middleValue) {
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*matchOrInsertionPoint = middle;
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return true;
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}
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if (target < 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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*matchOrInsertionPoint = 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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