C++ STL Algorithm Library

Algorithms are ready-made functions that help you perform common operations like searching, sorting, counting, and comparing on containers (like arrays, vectors, sets, etc.). These algorithms are defined in the <algorithm> and <numeric> header files.

Type of Algorithms

We can divide the algorithms into following parts:

1. Searching Algorithms

Searching algorithms are methods used to find a specific element or information in a data structure like an array, vector, or list.
They help locate an element efficiently without manually checking each item.

Some of the most frequently used searching algorithms are:

• find() : Searches for an element and returns its iterator if present.
• find_if() : Finds the first element satisfying a given condition.
• binary_search() : Checks if an element exists in a sorted container.
• lower_bound() : Returns an iterator to the first element not less than a given value.
• upper_bound() : Returns an iterator to the first element greater than a given value.
• count() : Counts occurrences of a specific value in a range.
• count_if() : Counts elements satisfying a given condition in a range.
• find_end() : Finds the last occurrences of a subsequence in a range.

2. Sorting and Rearranging Algorithms

These change the order or position of elements.

• sort() : Arranges elements in a given range into ascending order by default.
• stable_sort() : Sorts elements while preserving the relative order of equal elements.
• partial_sort() : Sorts only the first N elements in order, leaving the rest unsorted.
• nth_element() : Rearranges elements so the nth position has the correct element as in sorted order, with smaller ones before it and larger ones after it (but unordered).
• is_sorted() : Checks if the given range is already sorted in ascending order (or by custom comparator).
• is_sorted_until() : Returns an iterator to the first element where the sorted order breaks.

3.Manipulation Algorithms

These change or update values in the container without necessarily sorting or searching them.

• copy() : Copies element from one range into another range, preserving their order.
• copy_if() : Copies only the elements that satisfy a given condition to another range.
• copy_n() : Copies exactly n elements from a source range to a destination range.
• copy_backward() : Copies elements from a source range to a destination range in reverse order, starting from the end.
• move() : Transfers elements from a source range to a destination range, leaving the source elements in a valid but unspecified state.
• swap() : Exchanges the values of two elements.
• replace() : Replaces all occurrences of a specific value in a range with a new value.
• replace_if() : Replaces all elements that satisfy a given condition with a new value.
• remove() : moves all elements not equal to a given value to the front of the range and returns an iterator to the new logical end (does not actually reduce container size).
• fill() : Assigns a specified value to every element in a given range.
• transform() : Applies a function to each element in a range and stores the result in another range.
• generate() : Assigns values to a range by repeatedly calling a given function or generator.
• shuffle() : Randomly rearranges the elements in a given range.

4. Counting & Comparing Algorithms

These check or count elements based on conditions.

• count() : Returns the number of elements in a range that are equal to a specified value.
• count_if() : Returns the number of elements in a range that satisfy a given condition.
• equal() : Checks if two ranges have the same elements in the same order.
• mismatch() : Finds the first position where two ranges differ and returns iterators to the mismatched elements.
• lexicographical_compare() : Checks if one range is lexicographically less than another (like dictionary order).
• is_permutation() : Checks if one range is a permutation of another, i.e., contains the same elements in any order.