C Program to Check Number is Keith Number or Not

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Write a ‘C’ program to check if a number is Keith Number.

  • A Keith number is an n-digit integer (NUM>9) such that if a Fibonacci-like sequence (in which each term in the sequence is the sum of the n previous terms) is formed with the first n terms taken as the decimal digits of the number NUM, then NUM itself occurs as a term in the sequence.

Example:

75 – Keith number
7,5
7+5=12
5+12=17
12+17=29
17+29=46
29+46=75
75 Occurs in the generated sequence and so it is a Keith number.

341 – Not a Keith number
3, 4, 1
3+4+1=8, 
4+1+8=13, 
1+8+13=22, 
8+13+22=43, 
13+22+43=78, 
22+43+78=143
78+43+143=264
43+143+264=450
341 is not a Keith number since it will not occur in the generated sequence.

Input : ‘n’
Output : Yes / No
Constraints:
1 <= ‘n’ <= 10000000

Code:

# include <stdio.h>
# include <stdlib.h>


int lenCount(int nm)
{  int ctr=0;
    while(nm>0)
    {
        nm=nm/10;
        ctr++;
     }
     return ctr; 
}

int main()
{
    int num1=0,arr1[10],num2=0,flg=0,i=0,sum=0;
    scanf("%d",&num1);
    num2=num1;
    for(i=lenCount(num2)-1;i>=0;i--)
    {
        arr1[i]=num1 % 10;
        num1/=10;
    }
    while(flg==0)
    {
        for(i=0;i<lenCount(num2);i++)
            sum+=arr1[i];
        if(sum==num2)
        {
            printf("Yes");
            flg=1;
        }
        if(sum>num2)
        {
            printf("No");
            flg=1;
        }
        for(i=0;i<lenCount(num2);i++)
        {
            if(i!=lenCount(num2)-1)
                arr1[i]=arr1[i+1];
            else
                arr1[i]=sum;
        }
        sum=0;
    }
}
Code language: C/AL (cal)

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