STL Containers Inside Peter Sikachev Institute of Computer Graphics and Algorithms Vienna University...

transcript

STL Containers Inside

Peter Sikachev

Institute of Computer Graphics and Algorithms

Vienna University of Technology

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OverviewIntroductionIteratorsvectorlistset and mapPerformance Overview

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What is a Container?

Container is a class, a data structure, or an abstract data type whose instances are collections of other objects

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What is a Container?

Container is a class, a data structure, or an abstract data type whose instances are collections of other objects

std::vector<int> vecNumbers;

contiguous memory•vector•string•deque…

associative•set, map•multiset, multimap•hash_set…

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Types of the ContainersContainers

lists•list…

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Iterator

Iterator is an object that allows a programmer to traverse through all the elements of a collection, regardless of its specific implementation

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IteratorIterator

vector

elem elem

for (int* i = &Number[0]; i < &Number + Number.size(); i++){

*i = …;}

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IteratorIterator

vector

for (std::vector<int>::iterator i = Numbers.begin(); i < Numbers.end(); i++){

*i = …;}

elem elem

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IteratorIterator

vector list

for (std::list<int>::iterator i = Numbers.begin(); i < Numbers.end(); i++){

*i = …;}

nextprev

elemelem elem

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IteratorIterator

for (std::set<int>::iterator i = Numbers.begin(); i < Numbers.end(); i++){

*i = …;}

vector setlist

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Iterator CategoriesIterators

inputx=*i, ++

outputx=*i, ++

forward

bidirectional--

random acess+n, -n, += n, -= n, <, >, <=, >=

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Iterator Adapters•Insert•Reverse•Stream (for input and output)

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Iterator Adapters•Insert•Reverse•Stream (for input and output)

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Insertervalues

results

… … … …

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Inserter

int MultiplyByTen(int x);

vector <int> values;…vector <int> results;transform(values.begin(), values.end(),

results.end(), transmogrify);

values

results

… … … …

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Inserter

results.end(), transmogrify);

values

results

… … … …

Runtime error!

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Inserter

back_inserter(results), transmogrify);

values

results

… … … … 10 20 30

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Inserter

vector <int> values;…list <int> results;transform(values.begin(), values.end(),

front_inserter(results), transmogrify);

values

results

… … … …102030

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Inserter

vector <int> values;…list <int> results;transform(values.rbegin(), values.rend(),

front_inserter(results), transmogrify);

values

results

… … … …302010

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Inserter

inserter(results, results.begin() + results.size() / 2), transmogrify);

values

results

… … … …302010

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vector•“Growing Array”

elem elemelem

vecNumbers.size();

vecNumbers.capacity();

Costs•Find – O(n)•Insert – O(n)•Random Access – O(1)•Erase – O(n)

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elem elemelem

vecNumbers.size();

std::vector<int> vecNumbers;int k;…vecNumbers.push_back(k);

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elem elemelem

vecNumbers.size();

elem elem

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elem elemelem

vecNumbers.size();

elem elem elem

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elem elemelem

vecNumbers.size();

elem elem elem

What next?

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vector•Reallocation•New size may vary (typically 1.5-2 old size)•Problems?

elem elemelem elem elem elem elem

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Reallocation Problems•Copying (copy constructors)•Iterators invalidation•Unused capacity

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Avoiding Reallocationsstd::vector<int> vecNumbers;for (int i = 0; i < 1000; i++){

vecNumbers.push_back(…);}

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Avoiding Reallocationsstd::vector<int> vecNumbers;for (int i = 0; i < 1000; i++){

vecNumbers.push_back(i);}

Up to 18 reallocations!

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Avoiding Reallocationsstd::vector<int> vecNumbers;vecNumbers.reserve(1000);for (int i = 0; i < 1000; i++){

vecNumbers.push_back(i);}

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Unused Capacity

{vector<int>(vecNumbers.begin(),vecNumbers.end()).swap(vecNumbers);

•“The swap trick”

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“Swap Trick” Step-by-Step

•Create temporary object

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•Create temporary object•Initialize with the old vector values

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•Create temporary object•Initialize with the old vector values•Swap pointers

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•Create temporary object•Initialize with the old vector values•Swap pointers•Delete old vector

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Removing the Elements•It should be straightforward, isn’t it?

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Removing the Elements•It should be straightforward, isn’t it?

•No, it isn’t!

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Removing the Elementsvector <int> v;v.reserve(10);for (int i = 1; i <= 10; i++){

v.push_back(i);}

v[3] = v[5] = v[9] = 99;

remove(v.begin(), v.end(), 99);

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v.push_back(i);}

v[3] = v[5] = v[9] = 99;

991 2 3 5 99 7 8 9 99

v.begin() v.end()

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v.push_back(i);}

v[3] = v[5] = v[9] = 99;

vector <int>::iterator newEnd(remove(v.begin(), v.end(), 99));

51 2 3 7 8 9 ? ? ?

v.begin() v.end()

newEnd

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v.push_back(i);}

v[3] = v[5] = v[9] = 99;

51 2 3 7 8 9 8 9 99

v.begin() v.end()

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v.push_back(i);}

v[3] = v[5] = v[9] = 99;

v.erase(remove(v.begin(), v.end(), 99),v.end());

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v.begin() v.end()

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list•just a list (hence the name!)

Costs•Find – O(n)•Insert – O(1)•Random Access – O(n)•Erase – O(1)

nextprev

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Checking the Emptinessif (c.size() == 0)… if (c.empty())…

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bad good

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bad – O(n) good – O(1)

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Why?list <int> list1;list <int> list2;…list1.splice(

list1.end(), list2,find(list2.begin(), list2.end(), 5),find(list2.rbegin(), list2.rend(), 10).base()

/*move all nodes in list2 from the first occurrence of 5 through the last occurrence of 10 to the end of list1. “base()” converts a reverse_iterator into the “corresponding” iterator*/

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Why?list <int> list1;list <int> list2;…list1.splice(

list1.end(), list2,find(list2.begin(), list2.end(), 5),find(list2.rbegin(), list2.rend(), 10).base()

/*move all nodes in list2 from the first occurrence of 5 through the last occurrence of 10 to the end of list1. “base()” converts a reverse_iterator into the “corresponding” iterator*/

size unknown!

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set and map•Organized as a binary search tree

•node.value > node.leftSubtree.values•node.value < node.rightSubtree.values•both the left and right subtrees must also be binary search trees.

Costs•Find – O(log(n))•Insert – O(log(n))•Random Access(?) – O(log(n))•Erase – O(log(n))

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Inserting a new element

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Costs•Find – O(n)•Insert – O(n)•Random Access(?) – O(n)•Erase – O(n)

•Limiting subtree height is needed

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Red-Black Tree

1. A node is either red or black.2. The root is black.3. All leaves are black.4. Both children of every red node are black.5. Every simple path from a given node to any of its descendant

leaves contains the same number of black nodes.

=> height < 2 lg (n+1)

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Red-Black Tree

• New element added is red• Adding may violate ONLY rules 2 and 4• Rule 2 => just repaint• Otherwise…

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Red-Black Tree• Case 1

• Case 2(after that apply 3)

• Case 3

• The similar stuff for deleting

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Consequences• No key modifications in place!

STL Containers Inside Peter Sikachev Institute of Computer Graphics and Algorithms Vienna University...

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