Add Ugly Numbers (TheAlgorithms#2615)

skmodi649 · web-flow · commit 5dd3366edc89 · 2021-10-15T09:17:51.000+03:00
diff --git a/Maths/NthUglyNumber.java b/Maths/NthUglyNumber.java
@@ -0,0 +1,59 @@
+// 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.
+// By convention, 1 is included.
+// A program to find the nth Ugly number
+
+// Algorithm :
+// Initialize three-pointers two, three, and five pointing to zero.
+// Take 3 variables nm2, nm3, and nm5 to keep track of next multiple of 2,3 and 5.
+// Make an array of size n to store the ugly numbers with 1 at 0th index.
+// Initialize a variable next which stores the value of the last element in the array.
+// Run a loop n-1 times and perform steps 6,7 and 8.
+// Update the values of nm2, nm3, nm5 as ugly[two]*2, ugly[three]*3, ugly[5]*5 respectively.
+// Select the minimum value from nm2, nm3, and nm5 and increment the pointer related to it.
+// Store the minimum value in variable next and array.
+// Return next.
+
+
+
+package Maths;
+import java.util.*;
+class NthUglyNumber {
+    /* Function to get the nth ugly number*/
+    public long getNthUglyNo(int n) {
+        long[] ugly = new long[n];
+        int two=0, three=0, five=0;
+        long nm2=2, nm3=3, nm5=5;
+        long next = 1;
+
+        ugly[0] = 1;
+
+        for(int i=1; i<n; i++){
+            next = Math.min(nm2, Math.min(nm3, nm5));
+
+            ugly[i] = next;
+            if(next == nm2){
+                two = two+1;
+                nm2 = ugly[two]*2;
+            }
+            if(next == nm3){
+                three = three+1;
+                nm3 = ugly[three]*3;
+            }
+            if(next == nm5){
+                five = five+1;
+                nm5 = ugly[five]*5;
+            }
+        }
+        return next;
+    }
+
+    public static void main(String[] args)
+    {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the value of n : ");
+        int n = sc.nextInt();
+        NthUglyNumber ob = new NthUglyNumber();
+        long ugly = ob.getNthUglyNo(n);
+        System.out.println("nth Ugly number is : "+ugly);
+    }
+}
