#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>

int remove_value(std::deque<int>& dq, int value);

TEST_CASE("Removes all occurrences and returns correct count", "[remove_value]") {
    std::deque<int> dq = {1, 2, 3, 2, 4, 2, 5};
    int removed = remove_value(dq, 2);
    REQUIRE(removed == 3); // 3 elements should be removed
    REQUIRE(dq == std::deque<int>({1, 3, 4, 5})); // Remaining elements
}

TEST_CASE("Removes nothing if value not present", "[remove_value]") {
    std::deque<int> dq = {1, 3, 4, 5};
    int removed = remove_value(dq, 2);
    REQUIRE(removed == 0); // No elements removed
    REQUIRE(dq == std::deque<int>({1, 3, 4, 5})); // Unchanged
}

TEST_CASE("Removes all elements if all are equal to value", "[remove_value]") {
    std::deque<int> dq = {2, 2, 2};
    int removed = remove_value(dq, 2);
    REQUIRE(removed == 3); // All removed
    REQUIRE(dq.empty()); // Deque should be empty
}

TEST_CASE("Works with empty deque", "[remove_value]") {
    std::deque<int> dq;
    int removed = remove_value(dq, 2);
    REQUIRE(removed == 0); // Nothing to remove
    REQUIRE(dq.empty()); // Still empty
}

TEST_CASE("Removes only consecutive values", "[remove_value]") {
    std::deque<int> dq = {1, 2, 2, 3, 4, 2, 5, 2};
    int removed = remove_value(dq, 2);
    REQUIRE(removed == 4); // Four 2's
    REQUIRE(dq == std::deque<int>({1, 3, 4, 5}));
}

test.cpp

This course explains how iterators work in the C++ Standard Template Library and how they connect containers and algorithms. You will learn what iterators are, how different iterator categories behave, and how to use them safely and idiomatically with STL containers and algorithms. By the end of the course, you will confidently read, write, and reason about iterator-based code, including const iterators, reverse iterators, and iterator invalidation rules.

Learn the foundational concepts of iterators, their purpose in the STL, and how to use them for basic container traversal.

Delve into the different categories of iterators, their capabilities, and which containers support each category.

Investigate how iterators behave with different STL containers, including sequence and associative containers, and the importance of const iterators.

Learn how STL algorithms interact with iterators, how to use them safely, and how to avoid iterator invalidation.

Challenge: Safe Element Removal

Solution