Algoritmos Agit 2021

Professor Fabio Galuppo

https://www.agit.com.br/cursoalgoritmos.php

Dia 1 - 15/05/2021

Aula

Resolver os problemas

Arquivos .cpp programa driver, onde fica o main()
Arquivos .t.cpp classe de testes
Arquivos .hpp conteúdo principal

CTRL+D EOF do linux linear_search

cpp_feature_testing.cpp verificar compatibilidades do compilador

std::size_t

std::size_t == alias do unsigned long long, padrão dos containers

Day01/code/benchmark_linear_search.cpp

target = 42, 4096 42 1361, 4096 iterações procurando por 42, encontrou na posição 1361 target = 1001, 4096 1001 18446744073709551615 máximo do size_t - 1

Links úteis

Update GCC

https://gcc.gnu.org/

https://linuxize.com/post/how-to-install-gcc-compiler-on-ubuntu-18-04/

$ sudo apt install gcc-11 g++-11

$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 110 --slave /usr/bin/g++ g++ /usr/bin/g++-11 --slave /usr/bin/gcov gcov /usr/bin/gcov-11

$ sudo update-alternatives --config gccThere are 4 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path             Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gcc-11   110       auto mode
  1            /usr/bin/gcc-11   110       manual mode
  2            /usr/bin/gcc-7    70        manual mode
  3            /usr/bin/gcc-8    80        manual mode
  4            /usr/bin/gcc-9    90        manual mode

Press <enter> to keep the current choice[*], or type selection number: 

$ g++ --version
g++ (Ubuntu 11.1.0-1ubuntu1~18.04.1) 11.1.0

$ gcc --version
gcc (Ubuntu 11.1.0-1ubuntu1~18.04.1) 11.1.0

https://linuxize.com/post/how-to-install-gcc-on-ubuntu-20-04/

Dia 2 - 22/05/2021

Aula

https://msgpack.org/index.html

sbe simple binary encoding

Zero MQ

https://zeromq.org/get-started/?language=cpp#

i++ gera temporário

++i não gera temporário, boa prática

Usar emplace_back em vez de push_back https://www.cplusplus.com/reference/vector/vector/emplace_back/

http://www.cplusplus.com/reference/utility/move/

https://www.cplusplus.com/reference/set/set/set/

Layout da Memória

Day02/code/cpp_memory_layout.cpp

g++ -O3 cpp_memory_layout.cpp -o cpp_memory_layout.o

./cpp_memory_layout.o 

[ 8b]  140720460576096 (0x7ffc0910b560)       on stack
[ 4b]  140720460576108 (0x7ffc0910b56c):    1 on stack
[ 4b]  140720460576112 (0x7ffc0910b570):   42 on stack
[ 8b]  140720460576128 (0x7ffc0910b580)       on stack
[ 8b]  140720460576136 (0x7ffc0910b588)       on stack
[ 8b]  140720460576144 (0x7ffc0910b590)       on stack
[ 8b]  140720460576152 (0x7ffc0910b598)       on stack
[ 4b]  140720460576116 (0x7ffc0910b574):   84 on stack
[ 4b]  140720460576120 (0x7ffc0910b578):  126 on stack
[ 4b]  140720460576124 (0x7ffc0910b57c):  168 on stack
[24b]  140720460576160 (0x7ffc0910b5a0):    4 on stack
[ 4b]   94692382408304 (0x561f49d0fe70):   42 on heap
[ 4b]   94692382408336 (0x561f49d0fe90):   84 on heap
[ 4b]   94692382408368 (0x561f49d0feb0):  126 on heap
[ 4b]   94692382408400 (0x561f49d0fed0):  168 on heap
[ 4b]   94692382408432 (0x561f49d0fef0):   42 on heap
[ 4b]   94692382408436 (0x561f49d0fef4):   84 on heap
[ 4b]   94692382408440 (0x561f49d0fef8):  126 on heap
[ 4b]   94692382408444 (0x561f49d0fefc):  168 on heap
[ 4b]   94692358602788 (0x561f4865c024):    0 on data (uninitialized)
[ 4b]   94692358602792 (0x561f4865c028):    0 on data (uninitialized)
[ 4b]   94692358602772 (0x561f4865c014):   42 on data (initialized)
[ 4b]   94692358602768 (0x561f4865c010):   42 on data (initialized)
       140131755052800 (0x7f72f77b4f00):   printf on text
        94692356499536 (0x561f4845a850):     main on text
        94692356501168 (0x561f4845aeb0):    print on text

Resource Acquisition Is Initialization or RAII

Em 01:46:30

Day02/code/raii.hpp

Reservar o recurso no construtor e liberar o recurso no destrutor

Idioma para prevenção de leaks: memória, arquivos, sockets, threads, etc

O recurso é:

Aquirido pelo objeto na sua inicialização (constructor)
Mantido durante o tempo de vida do objeto
Liberado na destruição do objeto (destructor)

Object lifetime and resource management (RAII)

Dynamic Array (baseada em índice)

Em 02:09:45

Day02/code/dynamic_array.hpp

Sempre que tiver a possibilidade, passe um capacity. Ex: vector.reserve(). Melhora a performance.

 ./dynamic_array.o 
int: add an item, -: remove an item, ?: display data, !: display info
  dynamic_array<int> size:     1000 capacity:     1024
         vector<int> size:   100000 capacity:   131072
         vector<int> size:    10000 capacity:    16384
         vector<int> size:     1000 capacity:     1024
reserved vector<int> size:    10000 capacity:    10000
  dynamic_array<int> size:   100000 capacity:   131072
         vector<int> size:   100000 capacity:   131072
  dynamic_array<int> size:    10000 capacity:    16384
  dynamic_array<int> size:  1000000 capacity:  1048576
reserved vector<int> size:     1000 capacity:     1000
  dynamic_array<int> size:  1000000 capacity:  1048576
reserved vector<int> size:     1000 capacity:     1000
         vector<int> size:    10000 capacity:    16384
reserved vector<int> size:  1000000 capacity:  1000000
         vector<int> size:     1000 capacity:     1024
  dynamic_array<int> size:     1000 capacity:     1024
         vector<int> size:  1000000 capacity:  1048576
  dynamic_array<int> size:   100000 capacity:   131072
         vector<int> size:  1000000 capacity:  1048576
reserved vector<int> size:   100000 capacity:   100000
reserved vector<int> size:    10000 capacity:    10000
reserved vector<int> size:  1000000 capacity:  1000000
reserved vector<int> size:   100000 capacity:   100000
  dynamic_array<int> size:    10000 capacity:    16384
dynamic_array:
===============================================================================
   Name (baseline is *)   |   Dim   |  Total ms |  ns/op  |Baseline| Ops/second
===============================================================================
         bench_dynarr_add |    1000 |     0.006 |       5 |  0.378 |181061017.6
  bench_std_vec_push_back |    1000 |     0.011 |      10 |  0.730 | 93914350.1
 bench_std_vec_rsrvd_pb * |    1000 |     0.015 |      14 |      - | 68521310.1
         bench_dynarr_add |   10000 |     0.020 |       1 |  0.621 |512400082.0
  bench_std_vec_push_back |   10000 |     0.099 |       9 |  3.141 |101271976.0
 bench_std_vec_rsrvd_pb * |   10000 |     0.031 |       3 |      - |318126869.0
         bench_dynarr_add |  100000 |     0.856 |       8 |  4.010 |116772910.6
  bench_std_vec_push_back |  100000 |     2.431 |      24 | 11.384 | 41133592.4
 bench_std_vec_rsrvd_pb * |  100000 |     0.214 |       2 |      - |468254674.4
         bench_dynarr_add | 1000000 |    26.333 |      26 |  5.820 | 37975872.3
  bench_std_vec_push_back | 1000000 |     8.903 |       8 |  1.968 |112326572.0
 bench_std_vec_rsrvd_pb * | 1000000 |     4.524 |       4 |      - |221030475.0
===============================================================================

C++ Standards Support in GCC

Day02/code/dynamic_array_playground.cpp compile using -std=c++20 parameter

Tests and perceptions in Day02/code/dynamic_array_playground.cpp

Por que o ultimo valor volta zero?
Por que dois operators = e dois métodos data() ?

Node Based Stack (baseada em ponteiro)

Em 02:50:00

Day02/code/node_based_stack.hpp

./node_based_stack.o 
int: push an item, -: pop an item, ?: display top of stack, !: display info
      std::stack<int> size:     1000
node_based_stack<int> size:     1000
      std::stack<int> size:  1000000
      std::stack<int> size:    10000
      std::stack<int> size:    10000
      std::stack<int> size:     1000
      std::stack<int> size:   100000
      std::stack<int> size:   100000
      std::stack<int> size:  1000000
node_based_stack<int> size:    10000
node_based_stack<int> size:    10000
node_based_stack<int> size:   100000
node_based_stack<int> size:     1000
node_based_stack<int> size:  1000000
node_based_stack<int> size:   100000
node_based_stack<int> size:  1000000
node_based_stack:
===============================================================================
   Name (baseline is *)   |   Dim   |  Total ms |  ns/op  |Baseline| Ops/second
===============================================================================
    bench_nb_stack_push * |    1000 |     0.045 |      45 |      - | 22054607.2
     bench_std_stack_push |    1000 |     0.008 |       7 |  0.171 |129032258.1
    bench_nb_stack_push * |   10000 |     0.651 |      65 |      - | 15361525.8
     bench_std_stack_push |   10000 |     0.075 |       7 |  0.115 |133996167.7
    bench_nb_stack_push * |  100000 |     1.418 |      14 |      - | 70508535.8
     bench_std_stack_push |  100000 |     1.220 |      12 |  0.860 | 81965735.0
    bench_nb_stack_push * | 1000000 |    16.574 |      16 |      - | 60334238.4
     bench_std_stack_push | 1000000 |    14.623 |      14 |  0.882 | 68384817.0
===============================================================================

Linear Search

Equivalente ao find do STL

Em 02:57:57

Day02/code/linear_search.hpp

./linear_search.o 
collection size: 10
string: find an item, ?: display collection, !: display info
?
RAVZS HFKOD EOOUX LYBJS DRJSO MRCZX VOKOL LJMED FRPNU AHMRR 
DRJSO
found at 4
!
    size: 10
capacity: 16
   delta: 6
fst addr: 0x55ebc1445b10
linear_search:
===============================================================================
   Name (baseline is *)   |   Dim   |  Total ms |  ns/op  |Baseline| Ops/second
===============================================================================
 bench_dynarr_add_lsrch * |    1000 |     0.038 |      38 |      - | 26028787.8
       bench_vec_pb_lsrch |    1000 |     0.023 |      22 |  0.586 | 44383294.1
    bench_dynarr_add_find |    1000 |     0.036 |      36 |  0.942 | 27634997.0
        bench_vec_pb_find |    1000 |     0.024 |      23 |  0.617 | 42186972.7
 bench_dynarr_add_lsrch * |   10000 |     0.522 |      52 |      - | 19158446.1
       bench_vec_pb_lsrch |   10000 |     0.263 |      26 |  0.504 | 37990312.5
    bench_dynarr_add_find |   10000 |     0.452 |      45 |  0.866 | 22116798.8
        bench_vec_pb_find |   10000 |     0.231 |      23 |  0.443 | 43285358.7
 bench_dynarr_add_lsrch * |  100000 |     7.172 |      71 |      - | 13943362.9
       bench_vec_pb_lsrch |  100000 |     5.057 |      50 |  0.705 | 19774397.8
    bench_dynarr_add_find |  100000 |     6.992 |      69 |  0.975 | 14302748.9
        bench_vec_pb_find |  100000 |     4.632 |      46 |  0.646 | 21587497.0
 bench_dynarr_add_lsrch * | 1000000 |    63.629 |      63 |      - | 15716077.4
       bench_vec_pb_lsrch | 1000000 |    46.471 |      46 |  0.730 | 21518714.7
    bench_dynarr_add_find | 1000000 |    63.236 |      63 |  0.994 | 15813793.0
        bench_vec_pb_find | 1000000 |    45.559 |      45 |  0.716 | 21949662.0
===============================================================================

O iterator é capaz de desacoplar o container do algoritmo

Dia 3 - 29/05/2021

Aula

Lista ligada dupla
Ponteiros
Smart Pointers

Linear search - detalhes de implementação

Em 00:00:00

Day03/code/linear_search.hpp

Lista ligada dupla

Em 00:11:00

Day03/code/doubly_linked_list.hpp

Smart pointers

Day03/code/smart_ptr.hpp

Day03/code/doubly_linked_list_alt.hpp

Local Buffer Optimization (LBO)

Day03/code/dynamic_array_lbo.hpp

https://en.cppreference.com/w/cpp/language/union

G++ 11 error

$ g++ -O3 dynamic_array_lbo.t.cpp dynamic_array_lbo.cpp -o dynamic_array_lbo.o

 g++ -O3 dynamic_array_lbo.t.cpp dynamic_array_lbo.cpp -o dynamic_array_lbo.o
In file included from dynamic_array_lbo.t.cpp:6:
dynamic_array_lbo.hpp: In member function ‘void dynamic_array_lbo::dynamic_array<T>::move(dynamic_array_lbo::dynamic_array<T>&&)’:
dynamic_array_lbo.hpp:302:32: error: invalid use of incomplete type ‘class dynamic_array_lbo::dynamic_array<T>’
  302 |                 dynamic_array::~dynamic_array();
      |                                ^~~~~~~~~~~~~~
dynamic_array_lbo.hpp:62:11: note: declaration of ‘class dynamic_array_lbo::dynamic_array<T>’
   62 |     class dynamic_array final
      |           ^~~~~~~~~~~~~

G++ 9 works!

g++-9 -O3 dynamic_array_lbo.t.cpp dynamic_array_lbo.cpp -o dynamic_array_lbo.o

Regular types

STL

Recursão

Day03/code/lucas_numbers_memoization.t.cpp

Caso base e chamada da função

Dia 4 - 12/06/2021

Aula

Memorization

Em 00:00:00

Programação Dinãmica

Day04/code/water_recipient_filling_dp.t.cpp

Em 00:07:20

Merging

Day04/code/merging.hpp

Em 00:53:10

std::copy()

merge_copy --> std::merge

Inplace Merge

Day04/code/merging.hpp

Evita cópia (buffer extra)

Em 01:33:25

std::rotate() usa rotate left

inplace_merge --> std::inplace_merge

Mergesort - Dividir para conquistar (pode ser usado para paralelismo)

Day04/code/sorting_mergesort.hpp

Ordenação, estável, se ordenar por dois critérios, mantém a ordenação do primeiro critério, diferente quicksort ideal fazer primeira ordenação com quicksort e a segunda com o mergesort

Em 01:57:20

mergesort --> std:stable_sort()

std::stable_sort

Binary search

Day04/code/binary_search.hpp

Em 02:20:54

std::midpoint C++20

binary_search_leftmost --> std::lower_bound
binary_search_rightmost --> std::upper_bound

STL

Between

Day04/code/binary_search.hpp

Em 03:03:28

Iterators

Em 03:08:25

Generalização de ponteiro
Um objeto que aponta para algum elemento num container, array ou sequencia
Um par de iterators representa um intervalo fechado-aberto [begin, end]

5 categorias

InputIterator, leitura
OutputIterator, escrita
ForwardIterator, incrementa o iterator, itera para frente
BidirectionalIterator, incrementa/ decrementa o iterator, itera para frente e para trás
RandomAccessIterator, faz tudo e tem acesso ao índice

um ponteiro tem todos os requisitos de um RandomAccessIterator

Iterator

String Utilities

Day04/code/string_utilities.hpp

Usar GCC 9

g++-9 -O3 string_utilities.t.cpp string_utilities.cpp -o string_utilities.o

std::string

Em 03:31:00

is_sorted and iota_helper

Day05/code/is_sorted.cpp

Em 03:44:35

Input: 2 4 4 4 4 4 5 5 5 5 5 5 6 6 6 6 6 7 7 7 8 8 9 9 9 
Is sorted ascending: true

Input: 5 5 1 4 2 4 9 1 5 2 3 2 2 7 6 6 7 5 2 5 8 5 1 8 8 
Is sorted ascending: false

Input: 9 9 9 8 8 7 7 7 6 6 6 6 6 5 5 5 5 5 5 4 4 4 4 4 2 
Is sorted descending: true

Input: 9 9 9 8 8 7 7 7 6 6 6 6 6 5 5 5 5 5 5 4 4 4 4 4 2 
Is sorted descending: true

IOTA

std::iota

Day04/code/iota_helper.hpp

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 
20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 83 86 89 92 
14 11 57 58 42 88 31 36 69 58 14 17 26 79 51 57 94 33 61 90 62 72 90 25 65 
24 22 56 57 46 80 37 41 66 57 24 27 33 73 52 57 84 39 60 82 60 68 81 33 62

Dia 5 - 19/06/2021 - Heap, Priority Queue

Aula

Particionamento

Day05/code/partitioning.hpp

Em 00:00:00

std::partition

Insert sort

Day05/code/sorting_insertsort.hpp

Quick sort

Day05/code/sorting_quicksort.hpp

Stanility in sorting

Day05/code/stability_in_sorting.t.cpp

Heap

Day05/code/sorting_heapsort.hpp

Day05/code/unbounded_heap.hpp

Dia 6 - 26/06/2021 - Algoritmos

Analise de algoritmos

Day06/code/benchmarking_algorithms.t.cpp

Day06/code/estimated_running_time.t.cpp

Algoritmos Agit 2021

Dia 1 - 15/05/2021

std::size_t

Day01/code/benchmark_linear_search.cpp

Links úteis

Update GCC

Dia 2 - 22/05/2021

Layout da Memória

Resource Acquisition Is Initialization or RAII

Dynamic Array (baseada em índice)

Tests and perceptions in Day02/code/dynamic_array_playground.cpp

Node Based Stack (baseada em ponteiro)

Linear Search

Dia 3 - 29/05/2021

Linear search - detalhes de implementação

Lista ligada dupla

Smart pointers

Local Buffer Optimization (LBO)

G++ 11 error

G++ 9 works!

Regular types

Recursão

Dia 4 - 12/06/2021

Memorization

Programação Dinãmica

Merging

Inplace Merge

Mergesort - Dividir para conquistar (pode ser usado para paralelismo)

Binary search

STL

Between

Iterators

5 categorias

String Utilities

Usar GCC 9

is_sorted and iota_helper

IOTA

Dia 5 - 19/06/2021 - Heap, Priority Queue

Particionamento

Insert sort

Quick sort

Stanility in sorting

Heap

Dia 6 - 26/06/2021 - Algoritmos

Analise de algoritmos

Hashtables

Pilhas e Filas

Ring Buffer

Stack an queue STL

Dia 7 - 03/07/2021

Aulas

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