問題
Count integers from left through right, including both endpoints, that have no equal neighboring digits. Use their usual decimal writing with no leading zeroes. Zero and all other single-digit numbers qualify.
Implement counting_numbers(left, right).
Input
left: The first allowed value.
right: The last allowed value.
Output
Return how many values satisfy the rule.
制約
0 ≤ left ≤ right ≤ 10¹⁸. The range may be too large to inspect each integer individually.
例
入力：
left = 10
right = 15
期待される出力：
expected = 5入力：
long long left = 10;
long long right = 15;
期待される出力：
long long expected = 5;入力：
long left = 10;
long right = 15;
期待される出力：
long expected = 5;解説
Only 11 has equal neighboring digits. The other five numbers qualify.
入力：
left = 0
right = 9
期待される出力：
expected = 10入力：
long long left = 0;
long long right = 9;
期待される出力：
long long expected = 10;入力：
long left = 0;
long right = 9;
期待される出力：
long expected = 10;解説
All ten values have just one digit and therefore no equal neighbors.
解き方のヒント
まずは自分で考えてから、ヒントを 1 つずつ開いてみましょう。
ヒント 1
Count valid numbers up to each endpoint, then subtract to get the range answer.
ヒント 2
Digit DP fits because validity depends on adjacent digits and whether you have started the number.
ヒント 3
Leading zeros need special handling so that shorter numbers are counted correctly.
目安の計算量
O(k * 10 * states) time, O(k * states) extra space
参考資料
この課題はCodeUtility用に調整されています。上記の説明と制約に従ってください。