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1. In DigitCounter, the prev argument is set to 10 while started is false. What does 10 mean there?

The number N has 10 digits, so the walk stops earlyNo real digit has been placed yet, so a leading zero cannot block the first real digitThe digit 9 has wrapped around to 0The number being counted is 10

2. Why does go write its answer to memo_ only when tight is false?

A tight state is never reached more than once, so storing it would waste memoryThe memo has no slot for the tight flag, so the write would go past the end of the vectorA tight answer depends on the digits of N, which the memo key does not hold, so a free path could read a wrong saved valueTight states return before the loop, so they never reach the write

3. What does this program print? ``

cpp
#include <iostream>
#include <string>

bool ok(int x) {
    std::string s = std::to_string(x);
    for (std::size_t i = 1; i < s.size(); ++i)
        if (s[i] == s[i - 1]) return false;
    return true;
}

int main() {
    int count = 0;
    for (int x = 1; x <= 30; ++x) count += ok(x);
    std::cout << count << '\n';
}

``

30292819

4. What does this program print? ``

cpp
#include <iostream>

int main() {
    int count = 0;
    for (int x = 0; x <= 100; ++x) {
        int sum = x / 10 + x % 10;
        if (sum == 7) ++count;
    }
    std::cout << count << '\n';
}

``

79108

5. DigitCounter is built for a 19-digit N. How many slots does its memo_ vector hold?

Type a number.

Digit DP