C++ STL Revison Short

1. Containers a. Vector push_back(value): Adds an element at the end. pop_back(): Removes the last element. size(): Returns the number of elements. clear(): Removes all elements. at(index): Returns the element at index (throws out-of-range exception if invalid). front(): Returns the first element. back(): Returns the last element. empty(): Returns true if the vector is empty. insert(position, value): Inserts element at a specific position. erase(position): Removes element at the given position. begin(): Returns an iterator to the first element. end(): Returns an iterator past the last element.

b. Stack push(value): Pushes an element to the top. pop(): Removes the top element. top(): Returns the top element. empty(): Returns true if stack is empty. size(): Returns the number of elements.

c. Queue push(value): Adds an element to the end. pop(): Removes the front element. front(): Returns the front element. back(): Returns the last element. empty(): Returns true if queue is empty. size(): Returns the number of elements.

d. Deque (Double-Ended Queue) push_front(value): Adds element at the front. push_back(value): Adds element at the back. pop_front(): Removes element from the front. pop_back(): Removes element from the back. front(): Returns the front element. back(): Returns the back element. size(): Returns the number of elements. empty(): Returns true if deque is empty.

e. Set (Unique Elements) insert(value): Inserts an element. erase(value): Removes an element. find(value): Finds an element (returns iterator). size(): Returns the number of elements. empty(): Returns true if set is empty. count(value): Returns the count of elements (either 0 or 1). lower_bound(value): Returns the iterator to the first element not less than the given value. upper_bound(value): Returns the iterator to the first element greater than the given value.

f. Map (Key-Value Pairs) insert({key, value}): Inserts a key-value pair. erase(key): Removes the key-value pair. find(key): Finds an element by key (returns iterator). size(): Returns the number of elements. empty(): Returns true if map is empty. at(key): Returns the value associated with key (throws exception if not found). lower_bound(key): Returns the iterator to the first element not less than the given key. upper_bound(key): Returns the iterator to the first element greater than the given key.

g. Unordered Set insert(value): Inserts an element. erase(value): Removes an element. find(value): Finds an element. count(value): Returns the number of occurrences of the value.

h. Unordered Map insert({key, value}): Inserts a key-value pair. erase(key): Removes a key-value pair. find(key): Finds an element by key. at(key): Returns the value associated with key. count(key): Returns the number of occurrences of the key.

2. Algorithms a. Sorting sort(begin, end): Sorts the elements in ascending order. reverse(begin, end): Reverses the order of elements. partial_sort(begin, middle, end): Sorts the range [begin, middle) in ascending order. stable_sort(begin, end): Sorts elements while maintaining relative order of equal elements.

b. Searching binary_search(begin, end, value): Returns true if value exists in the range. lower_bound(begin, end, value): Returns an iterator to the first element not less than value. upper_bound(begin, end, value): Returns an iterator to the first element greater than value. find(begin, end, value): Returns an iterator to the first occurrence of value.

c. Min/Max min(a, b): Returns the smaller of two values. max(a, b): Returns the larger of two values. min_element(begin, end): Returns an iterator to the smallest element. max_element(begin, end): Returns an iterator to the largest element.

d. Accumulate accumulate(begin, end, init): Returns the sum of elements in a range. partial_sum(begin, end, result): Computes the partial sum of elements.

e. Other Algorithms next_permutation(begin, end): Re-arranges elements into the next lexicographically greater permutation. prev_permutation(begin, end): Re-arranges elements into the previous lexicographically smaller permutation. rotate(begin, middle, end): Rotates the range [begin, end) so that the first element becomes the element at position middle.

3. Other Important Functions a. Iterators begin(): Returns an iterator to the first element. end(): Returns an iterator to one past the last element. rbegin(): Returns a reverse iterator to the last element. rend(): Returns a reverse iterator to one before the first element.

b. Pair make_pair(a, b): Creates a pair. first: Returns the first element of the pair. second: Returns the second element of the pair.

4. Useful Utility Functions swap(a, b): Swaps two elements. fill(begin, end, value): Fills the range with the specified value. copy(begin, end, output_begin): Copies elements from one range to another. remove(begin, end, value): Removes all occurrences of value from the range. remove_if(begin, end, condition): Removes all elements satisfying the given condition.

#include <iostream>
#include <vector>
using namespace std;
int main() {   
 vector<int> vec;    
 vec.push_back(1);    
 vec.push_back(2);    
 vec.push_back(3);        
 for (int v : vec) {        
    cout << v << " ";    }  
    cout << "\\n";    
    vec.pop_back();    
    cout << "Size after pop: " << 
    vec.size() << "\\n";}

#include <iostream>
#include <map>
using namespace std;
int main() {    
map<int, string> m;    m
[1] = "One";    
m[2] = "Two";        
for (auto& entry : m) {        
cout << entry.first << ": " << 
entry.second << "\\n";    }}

#include <iostream>
#include <set>
using namespace std;

int main() {
    set<int> s;
    s.insert(10);
    s.insert(20);
    s.insert(10); // Duplicate element is ignored

    for (int elem : s) {
        cout << elem << " ";
    }
}

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {   
vector<int> vec = {5, 2, 8, 3, 1};  sort(vec.begin(), vec.end()); 
// Sorts in ascending order
    for (int v : vec) {        
    cout << v << " ";   
    }
}    

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin >> s;
    unordered_map<char, int> freq;
    for (char c : s)
        freq[c]++;

    for (auto &p : freq) {
        cout << p.first << " -> " << p.second << endl;
    }
    return 0;
}