add set

2026-04-19 23:51:58 +08:00
commit 56dbf441fa
1 changed files with 383 additions and 0 deletions
@@ -0,0 +1,383 @@
 * std::set empty initialization :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835132
 :END:
 ** Front
 Write C++ to create an empty std::set<int>
 ** Back
 #+begin_src c++
 std::set<int> s;
 #+end_src
 * std::set initializer list :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835127
 :END:
 ** Front
 Write C++ to create a std::set from initializer list {3, 1, 2}
 ** Back
 #+begin_src c++
 std::set<int> s = {3, 1, 2};  // contents: {1, 2, 3} (sorted!)
 #+end_src
 * std::set copy constructor :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835123
 :END:
 ** Front
 Write C++ to copy construct a std::set from existing set s2
 ** Back
 #+begin_src c++
 std::set<int> s1(s2);        // or: s1 = s2;
 std::set<int> s1 = s2;
 #+end_src
 * std::set from range :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835120
 :END:
 ** Front
 Write C++ to construct std::set from iterator range of another set
 ** Back
 #+begin_src c++
 std::set<int> s2(++s1.begin(), s1.end());
 #+end_src
 * std::set C++17 deduction :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835116
 :END:
 ** Front
 Write C++17 deduction guide to create set from another set
 ** Back
 #+begin_src c++
 std::set s3 = s2;  // deduces std::set<int>
 #+end_src
 * std::set insert return type :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835112
 :END:
 ** Front
 Write C++ to insert 5 into std::set and check if it succeeded
 ** Back
 #+begin_src c++
 auto [it, success] = s.insert(5);
 if (!success) {
    // already exists
 }
 #+end_src
 * std::set insert with hint :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835107
 :END:
 ** Front
 Write C++ to insert 5 near begin() as a hint
 ** Back
 #+begin_src c++
 s.insert(s.begin(), 5);  // returns iterator only (C++11+)
 #+end_src
 * std::set emplace vs insert :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835103
 :END:
 ** Front
 Write C++ to emplace {5, 6} directly into a std::set without copying
 ** Back
 #+begin_src c++
 s.emplace(5);      // constructs in-place
 s.emplace(std::piecewise_construct,
          std::forward_as_tuple(5),
          std::forward_as_tuple());
 #+end_src
 * std::set erase by key :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835099
 :END:
 ** Front
 Write C++ to erase key 5 from std::set and check count removed
 ** Back
 #+begin_src c++
 size_t n = s.erase(5);  // returns count erased (0 or 1)
 #+end_src
 * std::set erase by iterator :cpp:set:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835095
 :END:
 ** Front
 Write C++ to erase element at iterator it
 ** Back
 #+begin_src c++
 it = s.erase(it);  // returns iterator to next element
 #+end_src
 * std::set erase range :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835091
 :END:
 ** Front
 Write C++ to erase all elements from begin() to end()
 ** Back
 #+begin_src c++
 s.erase(s.begin(), s.end());  // clears entire set
 #+end_src
 * std::set find :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835088
 :END:
 ** Front
 Write C++ to check if key 5 exists in set using find()
 ** Back
 #+begin_src c++
 if (s.find(5) != s.end()) {
    // found
 }
 #+end_src
 * std::set count :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835084
 :END:
 ** Front
 Write C++ to check if key 5 exists using count() (set returns 0 or 1)
 ** Back
 #+begin_src c++
 if (s.count(5) == 1) {
    // exists
 }
 #+end_src
 * std::set contains (C++20) :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835079
 :END:
 ** Front
 Write C++20 to check if key 5 exists using contains()
 ** Back
 #+begin_src c++
 if (s.contains(5)) {
    // found
 }
 #+end_src
 * std::set extract (C++17) :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835075
 :END:
 ** Front
 Write C++ to extract key 5 from set and reinsert it
 ** Back
 #+begin_src c++
 auto node = s.extract(5);  // removes and returns node_handle
 s.insert(std::move(node));
 #+end_src
 * std::set merge (C++17) :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835072
 :END:
 ** Front
 Write C++ to merge elements from set s2 into s1
 ** Back
 #+begin_src c++
 s1.merge(s2);  // transfers matching elements from s2 to s1
 #+end_src
 * std::set begin/end iterators :cpp:set:iterators:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835067
 :END:
 ** Front
 Write C++ to iterate over all elements in std::set
 ** Back
 #+begin_src c++
 for (const auto& elem : s) {
    std::cout << elem << '\n';
 }
 // or with iterators:
 for (auto it = s.begin(); it != s.end(); ++it) {
    std::cout << *it << '\n';
 }
 #+end_src
 * std::set reverse iterators :cpp:set:iterators:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835062
 :END:
 ** Front
 Write C++ to iterate backwards through std::set
 ** Back
 #+begin_src c++
 for (auto it = s.rbegin(); it != s.rend(); ++it) {
    std::cout << *it << '\n';  // prints in descending order
 }
 #+end_src
 * std::set const_iterator :cpp:set:iterators:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835057
 :END:
 ** Front
 Write C++ to get const_iterator to first element
 ** Back
 #+begin_src c++
 std::set<int>::const_iterator it = s.cbegin();  // C++11+
 auto it = s.cbegin();  // auto also works
 #+end_src
 * std::set lower_bound :cpp:set:lookup:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835053
 :END:
 ** Front
 Write C++ to find first element >= 5 in std::set
 ** Back
 #+begin_src c++
 auto it = s.lower_bound(5);
 if (it != s.end() && *it == 5) {
    // found exact match
 }
 #+end_src
 * std::set upper_bound :cpp:set:lookup:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835049
 :END:
 ** Front
 Write C++ to find first element > 5 in std::set
 ** Back
 #+begin_src c++
 auto it = s.upper_bound(5);  // skips past all elements == 5
 #+end_src
 * std::set equal_range :cpp:set:lookup:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835045
 :END:
 ** Front
 Write C++ to get pair of iterators for elements matching 5
 ** Back
 #+begin_src c++
 auto [lo, hi] = s.equal_range(5);
 // lo = lower_bound(5), hi = upper_bound(5)
 if (lo != hi) {
    // found element(s)
 }
 #+end_src
 * std::set insert multiple from initializer list :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835042
 :END:
 ** Front
 Write C++ to insert multiple elements {1, 2, 3} at once
 ** Back
 #+begin_src c++
 s.insert({1, 2, 3});
 // or with pair return (C++17):
 auto [it, success] = s.insert({1, 2, 3});
 #+end_src
 * std::set key_comp and value_comp :cpp:set:observers:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835037
 :END:
 ** Front
 Write C++ to get the comparison object from std::set
 ** Back
 #+begin_src c++
 std::set<int>::key_compare comp = s.key_comp();
 std::set<int>::value_compare vcomp = s.value_comp();  // same for set
 #+end_src
 * std::set empty and size :cpp:set:capacity:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835032
 :END:
 ** Front
 Write C++ to check if set is empty and get size
 ** Back
 #+begin_src c++
 bool b = s.empty();
 size_t n = s.size();
 size_t max = s.max_size();
 #+end_src
 * std::set clear :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835028
 :END:
 ** Front
 Write C++ to remove all elements from std::set
 ** Back
 #+begin_src c++
 s.clear();  // equivalent to s.erase(s.begin(), s.end())
 #+end_src
 * std::set swap :cpp:set:retrieval:production:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835025
 :END:
 ** Front
 Write C++ to swap contents of two sets
 ** Back
 #+begin_src c++
 s1.swap(s2);  // or: s1.swap(s2);
 std::swap(s1, s2);
 #+end_src
 * std::set O(log n) operations summary :cpp:set:complexity:retrieval:understanding:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835020
 :END:
 ** Front
 What is the time complexity of insert, find, erase in std::set?
 ** Back
 O(log n) for all operations. std::set is implemented as a red-black tree.
 * std::set properties :cpp:set:retrieval:understanding:
 :PROPERTIES:
 :ANKI_NOTE_TYPE: Basic
 :ANKI_NOTE_ID: 1776613835015
 :END:
 ** Front
 What are the key properties of std::set?
 ** Back
 - No duplicate keys (use std::multiset for duplicates)
 - Keys are sorted (ascending by default)
 - Implemented as red-black tree
 - Elements cannot be modified through iterators (const)