Uglynumber-Find "ugly number"

Uglynumber is defined as a number that can be divisible only by 1,2,3,5.

Rule 1 is the first uglynumber; and so on, 1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 27 30 32 36 40 ...

Question 1, given a non-0 int integer, determines whether the ugly number

Divide this number by 2,3,5; see if it can be divisible; the judgment of dividing is by Hasdigit method, using decimal to judge

If it can be divisible, recursively, and divided by 2,3,5, until the judgment is complete.

1 /**2 * Ugly number13  * @authorRust Fisher4 * Judge The number whether ugly5  */6  Public classUglyNumber1 {7      Public Static BooleanHasdigit (Doubled) {8         returnD*10%10! = 0;9     }Ten     /** One      * @paramNum A      * @returnboolean whether num is ugly -      */ -      Public Static Booleanisugly (intnum) { the         if(Num <= 0) { -             return false; -         } -         if(num = = 1) { +             return true; -         } +         if(!hasdigit (num/2.0)) { A             if(Isugly (NUM/2)) { at                 return true; -             }         -         }  -         if(!hasdigit (num/3.0)) { -             if(Isugly (NUM/3)) { -                 return true; in             } -         } to         if(!hasdigit (num/5.0)) { +             if(Isugly (NUM/5)) { -                 return true; the             } *         } $ Panax Notoginseng         return false; -     } the     /** + * Find the nth ugly number A      * @paramN the      * @returnThe nth Ugly number +      */ -      Public Static intNthuglynumber (intN) { $         if(n <= 0) { $             return-1; -         } -         intCount = 0; the         inti = 0; -          while(Count <=N) {Wuyi             if(isugly (i)) { thecount++; -             } Wu             if(Count = =N) { -                  Break; About             } $i++; -              -         } -         returni; A     } +      the      Public Static voidMain (String args[]) { -         intCount = 0; $          for(inti = 0; I < 100; i++) { the             if(isugly (i)) { thecount++; theSystem.out.print (i + "\ T")); the             } -             if(Count = = 10) { inCount = 0; the System.out.println (); the             } About         } theSystem.out.println ("\nthe n-th ugly Numbers:"); theCount = 0; the          for(inti = 1; I < 21; i++) { +System.out.print (Nthuglynumber (i) + ""); -         } theSystem.out.println ("\ nthe output of nth ugly number in this way is inefficient");Bayi     } the}

Output:

1234568910121516182024252730323640454850546064727580819096The n-th Ugly numbers:1  2  3  4  5  6  8  9  (  36)-Ten  the output of nth ugly number in this way is inefficient.

Issue 2: Number of nth ugly number

For example, the 1th ugly number is 1, the second one is 2, the third is 3 ...

It is known that 1,2,3,5 is ugly number, then the numbers can be multiplied by 2,3,5, one by one backwards, until the nth

Set 3 cursors, the corresponding factor is 2,3,5, using the factor 21 times, Index2 plus a

1  Public classuglynumber2{2      Public Static intGetmin (intAintBintc) {3         intMin = a < b?a:b;4         returnMin < c?Min:c; 5     }6      Public Static intNthuglynumber (intN) {7         if(N < 1) {8             return-1;9         }Ten         intIndex2 = 0, index3 = 0, index5 = 0;//Three index One         int[] Uglynums =New int[n]; AUglynums[0] = 1; -         intNext = 1; -          while(Next <N) { theUglynums[next] = getmin (uglynums[index2]*2,uglynums[index3]*3,uglynums[index5]*5); -             if(Uglynums[next] = = uglynums[index2]*2) index2++;//find out which index should move -             if(Uglynums[next] = = uglynums[index3]*3) index3++;//Index Moving forward -             if(Uglynums[next] = = uglynums[index5]*5) index5++; +next++; -         } +         returnUglynums[next-1]; A     } at      -      Public Static voidMain (String args[]) { -          for(inti = 1; I < 21; i++) { -System.out.print (Nthuglynumber (i) + ""); -         } -     } in}

Output:

Outputs the first 20 ugly number

Uglynumber-Find "ugly number"