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1. What does this program print? ``

cpp
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

size_t longestAtMostK(const string& s, size_t k) {
    unordered_map<char, size_t> count;
    size_t distinct = 0;
    size_t best = 0;
    size_t left = 0;
    for (size_t right = 0; right < s.size(); ++right) {
        char c = s[right];
        if (count[c] == 0) ++distinct;
        ++count[c];
        while (distinct > k) {
            char out = s[left];
            --count[out];
            if (count[out] == 0) --distinct;
            ++left;
        }
        size_t length = right - left + 1;
        if (length > best) best = length;
    }
    return best;
}

int main() {
    cout << longestAtMostK("abaccc", 2) << "\n";
}

``

3546

2. Why does the program keep a separate distinct counter instead of using the size of the map?

Because size() cannot be called on an unordered_mapBecause a key with count 0 stays in the map, so size() never goes down when a letter leaves the windowBecause size() returns a signed int that cannot be compared with kBecause the map keeps only the letters that are inside the window

3. What is the name of the counter that tracks how many letters in the window have a count above zero?

Type your answer.

4. What does this program print? ``

cpp
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

long long countAtMostK(const string& s, size_t k) {
    unordered_map<char, size_t> count;
    size_t distinct = 0;
    size_t left = 0;
    long long total = 0;
    for (size_t right = 0; right < s.size(); ++right) {
        char c = s[right];
        if (count[c] == 0) ++distinct;
        ++count[c];
        while (distinct > k) {
            char out = s[left];
            --count[out];
            if (count[out] == 0) --distinct;
            ++left;
        }
        total += static_cast<long long>(right - left + 1);
    }
    return total;
}

long long countExactlyK(const string& s, size_t k) {
    return countAtMostK(s, k) - countAtMostK(s, k - 1);
}

int main() {
    cout << countExactlyK("aabbb", 2) << "\n";
}

``

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5. For the text aabacbebebe with k set to 2, which window is the longest valid one?

aabaaabcbebebebebe

Frequency windows