Write a program to check whether a given number is an ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7. Note that 1 is typically treated as an ugly number.
Naive Solution – Simulation
Divide the number by factor 2, 3 or 5 until it cannot be done. If the remainder is 1, then it is ugly number.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | class Solution { public: bool isUgly(int num) { if (num <= 0) return false; if (num == 1) return true; while (num > 1) { if (num % 2 == 0) { num /= 2; continue; } if (num % 3 == 0) { num /= 3; continue; } if (num % 5 == 0) { num /= 5; continue; } return false; } return true; } }; |
class Solution {
public:
bool isUgly(int num) {
if (num <= 0) return false;
if (num == 1) return true;
while (num > 1) {
if (num % 2 == 0) {
num /= 2;
continue;
}
if (num % 3 == 0) {
num /= 3;
continue;
}
if (num % 5 == 0) {
num /= 5;
continue;
}
return false;
}
return true;
}
};A better, shorter version could be done by only checking the 2, 3 and 5 factors: Algorithms to Determine a Ugly Number/Integer
See also: Teaching Kids Programming – Ugly Number Detection Algorithm
–EOF (The Ultimate Computing & Technology Blog) —
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