如何找到连续自然继承者的最长序列？

Question

Two consecutive integers are natural successors if the second is the successor of the first in the sequence of natural numbers (1 and 2 are natural successors). Write a program that reads a number N followed by N integers, and then prints the length of the longest sequence of consecutive natural successors.

import java.util.Scanner;

public class objects {
    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int x = scan.nextInt();
        int nmbr[] = new int[x];
        for(int f=0;f<nmbr.length;f++)
            nmbr[f]=scan.nextInt();
        int counter = 0;
        int max = 0;
        for (int i = 0; i < nmbr.length - 1; i++) {
            if (nmbr[i] == (nmbr[i + 1]-1))
                counter++;
            else
                counter = 0;
            if (counter > max)
                max = (counter+1);
        }
        System.out.println(max);
    }
}

Why is my code still printing the counter without adding one? I am not finding the mistake sample run:

     7 2 3 5 6 7 9 10 
     2

it is printing 2 instead of 3.

Answer 1

When you see the first number out of sequence, you should reset counter to 1, not 0 - as it's the start of a sequence with length at least 1. You then need to also change the code which changes max :

if (counter > max) {
    counter = max;
}

After all, you just want max to be the maximum value of counter .

(I would strongly recommend using braces for every if statement, by the way - it's easier to avoid mistakes that way.)

Answer 2

 import java.util.Scanner;

 public class objects {
     public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);
        int x = scan.nextInt();
        int nmbr[] = new int[x];
        for(int f=0;f<nmbr.length;f++) {
            nmbr[f]=scan.nextInt();
        }
        int counter = 0;
        int max = 0;
        for (int i = 0; i < nmbr.length - 1; i++) {
            if (nmbr[i] == (nmbr[i + 1]-1)) {
                counter++;
            } else {
                if (counter > max)
                    max = (counter+1);
                counter = 0;
            }
        }
        System.out.println(max);
    }
}

Just a minor error in your logic there, you were updating max every single time the counter was greater than max, so the next time if the sequence comes to an end, it actually fails to register as the longest sequence. Just reorder it as I have done and it works.

Answer 3

you don't take into account the first number, in this case 5

when i == 2 its the start of the sequence, however, nmbr[1] is 3 therfore counter will stil be 0

start the counter to be 1 (this is logic, since the smallest sequence is 1) you need to change the if to be:

import java.util.Scanner;

public class objects {
     public static void main(String[] args) {

         Scanner scan = new Scanner(System.in);
         int x = scan.nextInt();
         int nmbr[] = new int[x];
         for(int f=0;f<nmbr.length;f++)
             nmbr[f]=scan.nextInt();
         int counter = 1;
         int max = 1;
         for (int i = 0; i < nmbr.length - 1; i++) {
             if (nmbr[i] == (nmbr[i + 1]-1))
                 counter++;
             else
                 counter = 1;
             if (counter > max)
                 max = counter;
         }
         System.out.println(max);
    }
} 

Answer 4

Your maximum condition is incorrect:

if (counter > max)
    max = (counter+1);

You compare max with counter and assign counter+1 . This way when max is equal to 2 it can't be updated with 2+1.

Probably you should use:

if (counter + 1 > max)
    max = (counter+1);    

PS: Your question doesn't show research effort. You could use debug output to understand what is going on with your program. Simplistic example:

for (int i = 0; i < nmbr.length - 1; i++) {
    if (nmbr[i] == (nmbr[i + 1]-1))
        counter++;
    else
        counter = 0;
    System.out.println("Current value: "+counter);
    if (counter > max) {
        max = (counter+1);
        System.out.println("New max value: "+max);
    }
}

Answer 5

Start your conter from 1. because if you start from 0 then it means you are not counting the 1st value.

else
    counter = 1;

And Change the dont increment your counter when assigning to max.

max =counter;

Answer 6

This was an easy one and already pointed out in previous answers you are wrongly setting the value of counter in your code.

Run your code through a debugger to keep a track of variable values of what you are expecting from your program versus what you are actually getting.

Stepping through each line of code can help you understand your mistakes better.