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Consecutive sequenced numbers in a string

  • Difficulty Level : Medium
  • Last Updated : 18 Jan, 2022

Given a string that contains only numeric digits, we need to check whether that strings contains numbers in consecutive sequential manner in increasing order. 
Note: Negative numbers are not considered part of this problem. So we consider that input only contains positive integer.
Examples: 
 

Input :  str = "1234"
Output : Yes 
         1
Explanation : 
There are 1, 2, 3, 4 which are 
consecutive and in increasing order.
And the starting number is 1

Input :  str = "91012"
Output : No
Explanation : 
There are no such sequence in the
string. 

Input :  str = "99100"
Output : Yes 
         99
Explanation : The consecutive sequential 
numbers are 99, 100

Input :  str = "010203"
Output : NO 
Explanation : 
Although at first glance there seems to
be 01, 02, 03. But those wouldn't be 
considered a number. 01 is not 1  it's 0, 1 

 

Approach: An easily implementable and useful approach is to start taking one character at first (assuming that our string start with 1 digit number) and then form a new string by concatenating the next number until the length of new string is equal to original string. 
Perhaps an example may clarify : 
Lets take string “99100” 
 

 

C++




// CPP Program to check whether a string contains
// consecutive sequential numbers or not
#include <iostream>
using namespace std;
 
// function to check consecutive sequential number
int isConsecutive(string str)
{
    // variable to store starting number
    int start;
 
    // length of the input string
    int length = str.size();
 
    // find the number till half of the string
    for (int i = 0; i < length / 2; i++) {
 
        // new string containing the starting
        // substring of input string
        string new_str = str.substr(0, i + 1);
 
        // converting starting substring into number
        int num = atoi(new_str.c_str());
 
        // backing up the starting number in start
        start = num;
 
        // while loop until the new_string is
        // smaller than input string
        while (new_str.size() < length) {
 
            // next number
            num++;
 
            // concatenate the next number
            new_str = new_str + to_string(num);
        }
 
        // check if new string becomes equal to
        // input string
        if (new_str == str)
           return start;
    }
 
    // if string doesn't contains consecutive numbers
    return -1;
}
 
// Driver's Code
int main()
{
    string str = "99100";
    cout << "String: " << str << endl;
    int start = isConsecutive(str);
    if (start != -1)
        cout << "Yes \n" << start << endl;
    else
        cout << "No" << endl;
 
    string str1 = "121315";
    cout << "\nString: " << str1 << endl;
    start = isConsecutive(str1);
    if (start != -1)
        cout << "Yes \n" << start << endl;
    else
        cout << "No" << endl;
 
    return 0;
}

Java




// Java Program to check whether a String contains
// consecutive sequential numbers or not
class GFG
{
 
// function to check consecutive sequential number
static int isConsecutive(String str)
{
    // variable to store starting number
    int start;
 
    // length of the input String
    int length = str.length();
 
    // find the number till half of the String
    for (int i = 0; i < length / 2; i++)
    {
 
        // new String containing the starting
        // substring of input String
        String new_str = str.substring(0, i + 1);
 
        // converting starting substring into number
        int num = Integer.parseInt(new_str);
 
        // backing up the starting number in start
        start = num;
 
        // while loop until the new_String is
        // smaller than input String
        while (new_str.length() < length)
        {
 
            // next number
            num++;
 
            // concatenate the next number
            new_str = new_str + String.valueOf(num);
        }
 
        // check if new String becomes equal to
        // input String
        if (new_str.equals(str))
        return start;
    }
 
    // if String doesn't contains consecutive numbers
    return -1;
}
 
// Driver Code
public static void main(String[] args)
{
    String str = "99100";
    System.out.println("String: " + str);
    int start = isConsecutive(str);
    if (start != -1)
        System.out.println("Yes \n" + start);
    else
        System.out.println("No");
 
    String str1 = "121315";
    System.out.println("\nString: " + str1);
    start = isConsecutive(str1);
    if (start != -1)
        System.out.println("Yes \n" + start);
    else
        System.out.println("No");
    }
}
 
// This code contributed by Rajput-Ji

Python3




# Python Program to check whether a String contains
# consecutive sequential numbers or not
 
# function to check consecutive sequential number
def isConsecutive(strs):
   
    # variable to store starting number
    start = 0;
 
    # length of the input String
    length = len(strs);
 
    # find the number till half of the String
    for i in range(length // 2):
 
        # new String containing the starting
        # substring of input String
        new_str = strs[0: i + 1];
 
        # converting starting substring into number
        num = int(new_str);
 
        # backing up the starting number in start
        start = num;
 
        # while loop until the new_String is
        # smaller than input String
        while (len(new_str) < length):
            # next number
            num += 1;
 
            # concatenate the next number
            new_str = new_str + str(num);
 
        # check if new String becomes equal to
        # input String
        if (new_str==(strs)):
            return start;
 
    # if String doesn't contains consecutive numbers
    return -1;
 
# Driver Code
if __name__ == '__main__':
    str0 = "99100";
    print("String: " + str0);
    start = isConsecutive(str0);
    if (start != -1):
        print("Yes \n" , start);
    else:
        print("No");
 
    str1 = "121315";
    print("\nString: " , str1);
    start = isConsecutive(str1);
    if (start != -1):
        print("Yes \n" , start);
    else:
        print("No");
 
# This code is contributed by shikhasingrajput

C#




// C# Program to check whether a String contains
// consecutive sequential numbers or not
using System;
 
class GFG
{
 
// function to check consecutive sequential number
static int isConsecutive(String str)
{
    // variable to store starting number
    int start;
 
    // length of the input String
    int length = str.Length;
 
    // find the number till half of the String
    for (int i = 0; i < length / 2; i++)
    {
 
        // new String containing the starting
        // substring of input String
        String new_str = str.Substring(0, i + 1);
 
        // converting starting substring into number
        int num = int.Parse(new_str);
 
        // backing up the starting number in start
        start = num;
 
        // while loop until the new_String is
        // smaller than input String
        while (new_str.Length < length)
        {
 
            // next number
            num++;
 
            // concatenate the next number
            new_str = new_str + String.Join("",num);
        }
 
        // check if new String becomes equal to
        // input String
        if (new_str.Equals(str))
        return start;
    }
 
    // if String doesn't contains consecutive numbers
    return -1;
}
 
// Driver Code
public static void Main(String[] args)
{
    String str = "99100";
    Console.WriteLine("String: " + str);
    int start = isConsecutive(str);
    if (start != -1)
        Console.WriteLine("Yes \n" + start);
    else
        Console.WriteLine("No");
 
    String str1 = "121315";
    Console.WriteLine("\nString: " + str1);
    start = isConsecutive(str1);
    if (start != -1)
        Console.WriteLine("Yes \n" + start);
    else
        Console.WriteLine("No");
    }
}
 
// This code has been contributed by 29AjayKumar

Javascript




<script>
 
// JavaScript Program to check whether a String contains
// consecutive sequential numbers or not
 
// function to check consecutive sequential number
function isConsecutive(str)
{
    // variable to store starting number
    let start;
   
    // length of the input String
    let length = str.length;
   
    // find the number till half of the String
    for (let i = 0; i < length / 2; i++)
    {
   
        // new String containing the starting
        // substring of input String
        let new_str = str.substring(0, i + 1);
   
        // converting starting substring into number
        let num = parseInt(new_str);
   
        // backing up the starting number in start
        start = num;
   
        // while loop until the new_String is
        // smaller than input String
        while (new_str.length < length)
        {
   
            // next number
            num++;
   
            // concatenate the next number
            new_str = new_str + (num).toString();
        }
   
        // check if new String becomes equal to
        // input String
        if (new_str == (str))
        return start;
    }
   
    // if String doesn't contains consecutive numbers
    return -1;
}
 
// Driver Code
let str = "99100";
document.write("String: " + str+"<br>");
let start = isConsecutive(str);
if (start != -1)
    document.write("Yes <br>" + start+"<br>");
else
    document.write("No<br>");
 
let str1 = "121315";
document.write("<br>String: " + str1+"<br>");
start = isConsecutive(str1);
if (start != -1)
    document.write("Yes <br>" + start+"<br>");
else
    document.write("No<br>");
 
 
 
// This code is contributed by rag2127
 
</script>
Output: 
String: 99100
Yes 
99

String: 121315
No

 


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