Problème
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.
Contraintes
0 ≤ left ≤ right ≤ 10¹⁸. The range may be too large to inspect each integer individually.
Exemples
Entrée :
left = 10
right = 15
Sortie attendue :
expected = 5Entrée :
long long left = 10;
long long right = 15;
Sortie attendue :
long long expected = 5;Entrée :
long left = 10;
long right = 15;
Sortie attendue :
long expected = 5;Explication
Only 11 has equal neighboring digits. The other five numbers qualify.
Entrée :
left = 0
right = 9
Sortie attendue :
expected = 10Entrée :
long long left = 0;
long long right = 9;
Sortie attendue :
long long expected = 10;Entrée :
long left = 0;
long right = 9;
Sortie attendue :
long expected = 10;Explication
All ten values have just one digit and therefore no equal neighbors.
Comment l'aborder
Essayez d'abord seul, puis ouvrez les indices un par un.
Indice 1
Count valid numbers up to each endpoint, then subtract to get the range answer.
Indice 2
Digit DP fits because validity depends on adjacent digits and whether you have started the number.
Indice 3
Leading zeros need special handling so that shorter numbers are counted correctly.
Complexité attendue
O(k * 10 * states) time, O(k * states) extra space
Références
Ce défi a été adapté pour CodeUtility. Suivez l'énoncé et les contraintes ci-dessus.