CC-7 : Check if number is fascinating.

Description:

For a number num, if we add 2*num and 3*num to num, then if the resultant number contains all digits from 1 to 9 only once, then the number num is said to be fascinating. Given number num as input, return true if num is fascinating, else return false.

Test cases and expected outputs:

Input Parameters	Expected outputs
The input number is: 273	273 is a fascinating number
The input number is: 219	219 is a fascinating number
The input number is: 999	999 is not a fascinating number

Pseudocode:

The java method should accept following input parameters: num (integer).

Initialize a StringBuilder sb.

Append num, 2*num, 3*num to sb.

Initialize a char array chars and set it to extracted characters from sb.

Initialize a variable intCntMap of type HashMap to hold characters from chars and their counts.

Iterate through chars using a for loop with idx as a loop variable with initial value 0 and increment idx till it reaches chars.length-1:

If intCntMap does not contain key equal to chars[idx]:

Add key chars[idx] and add value 1 to intCntMap.

If intCntMap contains key equal to chars[idx]:

Add key chars[idx]and add value equal to current value of key chars[idx], incremented by 1 to intCntMap.

After completion of above loop, intCntMap contains all digits of sb as keys and the counts of these digits in sb as values.

Using a for loop with idx as a loop variable with initial value 1 and increment idx till it reaches 9:

If intCntMap does not contain key idx and value 1, return false from the program.

If the above loop completes successfully till idx 9 without returning false from the program, that means the num is a fascinating number, so return true.

Code:

public boolean hashMapChkFascinating(int num1) throws Exception{
	int num2=2*num1;
	int num3=3*num1;
	StringBuilder sb=new StringBuilder();
	sb.append(num1);
	sb.append(num2);
	sb.append(num3);
	System.out.println("\n\nThe appended number is: "+sb.toString());
	char[] chars=new char[sb.length()];
	sb.getChars(0, sb.length(), chars, 0);
	HashMap< Character,Integer> intCntMap=new HashMap<Character, Integer>();
	for (int idx=0; idx < chars.length; idx++) {
		intCntMap.put(chars[idx], intCntMap.getOrDefault(chars[idx],0)+1);
	}
	if (intCntMap.get('0') != null) {return false;}
	char c;
	for (int idx=1; idx <= 9; idx++) {
		c=Character.forDigit(idx, 10);
		if (intCntMap.getOrDefault(c,0)!=1) {
			return false;
		}		
	}
	return true;		
}

Click here to download and run code and test cases !

Below fully running code can be copied and run on Eclipse or other Java IDEs. Refer the classname in code below. If the class name below is "A", save the code below to a file named A.java before running it. Be sure to try your own test cases to enhance your understanding ! You can also tweak the code to optimize or add enhancements and custom features.

import java.util.HashMap;


public class HashMapChkFascinating {
	
public boolean hashMapChkFascinating(int num1) throws Exception{
	int num2=2*num1;
	int num3=3*num1;
	StringBuilder sb=new StringBuilder();
	sb.append(num1);
	sb.append(num2);
	sb.append(num3);
	System.out.println("\n\nThe appended number is: "+sb.toString());
	char[] chars=new char[sb.length()];
	sb.getChars(0, sb.length(), chars, 0);
	HashMap< Character,Integer> intCntMap=new HashMap<Character, Integer>();
	for (int idx=0; idx < chars.length; idx++) {
		intCntMap.put(chars[idx], intCntMap.getOrDefault(chars[idx],0)+1);
	}
	if (intCntMap.get('0') != null) {return false;}
	char c;
	for (int idx=1; idx <= 9; idx++) {
		c=Character.forDigit(idx, 10);
		if (intCntMap.getOrDefault(c,0)!=1) {
			return false;
		}		
	}
	return true;		
}
	
	
    
public static void main(String[] args) {
	
	HashMapChkFascinating hp=new HashMapChkFascinating();
	boolean retVal;
	try {
	int num=273;
	System.out.println("\n\nThe input number is: "+num);
	retVal=hp.hashMapChkFascinating(num);
	if (retVal==true) {
	System.out.println("\n"+num+" is a fascinating number");
	}else {
	System.out.println("\n"+num+" is *not* a fascinating number");
	}
			
			
	num=219;
	System.out.println("\n\nThe input number is: "+num);
	retVal=hp.hashMapChkFascinating(num);
	if (retVal==true) {
	System.out.println("\n"+num+" is a fascinating number");
	}else {
	System.out.println("\n"+num+" is *not* a fascinating number");
	}
			
	num=999;
	System.out.println("\n\nThe input number is: "+num);
	retVal=hp.hashMapChkFascinating(num);
	if (retVal==true) {
	System.out.println("\n"+num+" is a fascinating number");
	}else {
	System.out.println("\n"+num+" is *not* a fascinating number");
	}
						
						
	}catch (Exception exception) {
	System.out.print("Exception: "+ exception);
    }
}


}