Enumeration algorithms provide a straightforward method for solving constraint-based numerical problems. When processing a range of integers to identify values containing specific digits, modulo arithmetic efficiently isolates each decimal place. The following implementation accumulates the sum of all numbers up to a given limit that contain 0, 1, 2, or 9.

#include <iostream>

bool contains_target_digits(int value) {
    int temp = value;
    while (temp > 0) {
        int digit = temp % 10;
        if (digit == 0 || digit == 1 || digit == 2 || digit == 9) {
            return true;
        }
        temp /= 10;
    }
    return false;
}

int main() {
    int limit;
    std::cin >> limit;
    long long total = 0;
    for (int current = 1; current <= limit; ++current) {
        if (contains_target_digits(current)) {
            total += current;
        }
    }
    std::cout << total << std::endl;
    return 0;
}

String analysis tasks often require parsing unstructured input and tracking character ocurrences. A stream-based parser can tokenize the input line into individual characters, which are then stored in a dynamic buffer. A map correlates each character with its occurrence count. Iterating through the map identifies the dominant character without requiring secondary sorting operations, reducing both code complexity and runtime overhead.

#include <iostream>
#include <string>
#include <sstream>
#include <map>
#include <vector>

int main() {
    std::string raw_input;
    std::getline(std::cin, raw_input);

    std::stringstream parser(raw_input);
    char token;
    std::vector<char> char_buffer;

    while (parser >> token) {
        char_buffer.emplace_back(token);
    }

    std::map<char, int> counts;
    for (char c : char_buffer) {
        counts[c]++;
    }

    char top_char = '\0';
    int top_freq = 0;

    for (const auto& pair : counts) {
        if (pair.second > top_freq) {
            top_freq = pair.second;
            top_char = pair.first;
        }
    }

    std::cout << top_char << '\n' << top_freq << std::endl;
    return 0;
}

Several C++ Standard Library components streamline these operations. Sorting contiguous containers utilizes std::sort with comparator functors:

#include <algorithm>
#include <vector>

std::vector<int> dataset = {4, 1, 8, 3};
// Ascending order
std::sort(dataset.begin(), dataset.end(), std::less<int>());
// Descending order
std::sort(dataset.begin(), dataset.end(), std::greater<int>());

Parsing strings into character buffers leverages std::stringstream to handle whitespace and type conversion seamlessly:

std::string text = "example";
std::stringstream stream(text);
char ch;
std::vector<char> chars;
while (stream >> ch) {
    chars.push_back(ch);
}

Converting string representations to numeric types follows the same extraction pattern:

std::string numeric_str = "5821";
std::stringstream converter(numeric_str);
int result;
converter >> result;

Reading an unknown quantity of integers untill a newline terminator requires checking the input stream state:

std::vector<int> numbers;
int val;
while (std::cin >> val) {
    numbers.push_back(val);
    if (std::cin.get() == '\n') break;
}

Range-based loops with auto simplify iteration over dynamic containers:

for (const auto& item : numbers) {
    std::cout << item << " ";
}

Linear lists represent a fundameental abstract data type where elements maintain a strict sequential relationship. Sequential lists implement this abstraction using contiguous memory blocks. Static allocation reserves a fixed-size array at compile time, simplifying memory management but limiting scalability.

#include <iostream>

constexpr int STATIC_CAPACITY = 50;

struct StaticSeqList {
    int elements[STATIC_CAPACITY];
    int current_len;
};

void initialize_static(StaticSeqList& list) {
    list.current_len = 0;
    for (int i = 0; i < STATIC_CAPACITY; ++i) {
        list.elements[i] = 0;
    }
}

int main() {
    StaticSeqList seq;
    initialize_static(seq);
    return 0;
}

Dynamic allocation overcomes fixed capacity constraints by requesting heap memory at runtime. The structure maintains a pointer to the data buffer, the current element count, and the allocated capacity. When the buffer reaches capacity, a reallocation routine provisions a larger memory block, migrates existing elements, updates the capacity metric, and releases the previous allocation.

#include <cstdlib>
#include <iostream>

struct DynamicSeqList {
    int* buffer;
    int current_len;
    int capacity;
};

void initialize_dynamic(DynamicSeqList& list, int initial_cap) {
    list.buffer = static_cast<int*>(std::malloc(initial_cap * sizeof(int)));
    list.current_len = 0;
    list.capacity = initial_cap;
}

void expand_capacity(DynamicSeqList& list, int additional) {
    int* old_buffer = list.buffer;
    list.buffer = static_cast<int*>(std::malloc((list.capacity + additional) * sizeof(int)));

    for (int i = 0; i < list.current_len; ++i) {
        list.buffer[i] = old_buffer[i];
    }

    list.capacity += additional;
    std::free(old_buffer);
}

int main() {
    DynamicSeqList dyn_seq;
    initialize_dynamic(dyn_seq, 10);
    expand_capacity(dyn_seq, 5);
    std::free(dyn_seq.buffer);
    return 0;
}