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The Algorithms

Keith Number

package com.thealgorithms.maths;

import java.util.*;

class KeithNumber {

    //user-defined function that checks if the given number is Keith or not
    static boolean isKeith(int x) {
        //List stores all the digits of the X
        ArrayList<Integer> terms = new ArrayList<Integer>();
        //n denotes the number of digits
        int temp = x, n = 0;
        //executes until the condition becomes false
        while (temp > 0) {
            //determines the last digit of the number and add it to the List
            terms.add(temp % 10);
            //removes the last digit
            temp = temp / 10;
            //increments the number of digits (n) by 1
        //reverse the List
        int next_term = 0, i = n;
        //finds next term for the series
        //loop executes until the condition returns true
        while (next_term < x) {
            next_term = 0;
            //next term is the sum of previous n terms (it depends on number of digits the number has)
            for (int j = 1; j <= n; j++) {
                next_term = next_term + terms.get(i - j);
        //when the control comes out of the while loop, there will be two conditions:
        //either next_term will be equal to x or greater than x
        //if equal, the given number is Keith, else not
        return (next_term == x);

    //driver code
    public static void main(String[] args) {
        Scanner in = new Scanner(;
        int n = in.nextInt();
        if (isKeith(n)) {
            System.out.println("Yes, the given number is a Keith number.");
        } else {
            System.out.println("No, the given number is not a Keith number.");