60 lines
1.9 KiB
Java
60 lines
1.9 KiB
Java
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// Ugly numbers are numbers whose only prime factors are 2, 3 or 5. The sequence 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, … shows the first 11 ugly numbers.
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// By convention, 1 is included.
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// A program to find the nth Ugly number
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// Algorithm :
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// Initialize three-pointers two, three, and five pointing to zero.
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// Take 3 variables nm2, nm3, and nm5 to keep track of next multiple of 2,3 and 5.
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// Make an array of size n to store the ugly numbers with 1 at 0th index.
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// Initialize a variable next which stores the value of the last element in the array.
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// Run a loop n-1 times and perform steps 6,7 and 8.
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// Update the values of nm2, nm3, nm5 as ugly[two]*2, ugly[three]*3, ugly[5]*5 respectively.
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// Select the minimum value from nm2, nm3, and nm5 and increment the pointer related to it.
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// Store the minimum value in variable next and array.
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// Return next.
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package Maths;
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import java.util.*;
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class NthUglyNumber {
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/* Function to get the nth ugly number*/
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public long getNthUglyNo(int n) {
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long[] ugly = new long[n];
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int two=0, three=0, five=0;
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long nm2=2, nm3=3, nm5=5;
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long next = 1;
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ugly[0] = 1;
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for(int i=1; i<n; i++){
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next = Math.min(nm2, Math.min(nm3, nm5));
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ugly[i] = next;
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if(next == nm2){
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two = two+1;
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nm2 = ugly[two]*2;
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}
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if(next == nm3){
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three = three+1;
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nm3 = ugly[three]*3;
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}
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if(next == nm5){
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five = five+1;
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nm5 = ugly[five]*5;
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}
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}
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return next;
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}
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public static void main(String[] args)
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{
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Scanner sc = new Scanner(System.in);
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System.out.println("Enter the value of n : ");
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int n = sc.nextInt();
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NthUglyNumber ob = new NthUglyNumber();
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long ugly = ob.getNthUglyNo(n);
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System.out.println("nth Ugly number is : "+ugly);
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}
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}
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