Missing Number In Sequence

A set of numbers which are in sequence are arranged in descending order as a string S. But one of the number in the sequence is missing in between in the string S. This string S is passed as input to the program. The program must identify the missing number M and print it as output.

Input Format:
The first line will contain the set of numbers in the sequence.

Boundary Conditions:
1 <= M <= 99999
Length of string S is from 5 to 200.

Output Format:
The first line will contain the missing number M.

Example Input/Output 1:

Input:
98764321

Output:
5

Explanation:
The numbers a sequence in descending order are 9 8 7 6 5 4 3 2 1. As 5 is missing, it is printed as the output.

Example Input/Output 2:

Input:
601600598597596

Output:
599

Explanation:
The numbers a sequence in descending order are 601 600 599 598 597 596. As 599 is missing, it is printed as the output.

#include <stdio.h>
long int n(char *a){
    long int b=0;
    for(int i=0;i<strlen(a);i++){
        if(isdigit(a[i])&&a[i])
            b=b*10+a[i]-'0';
        }
        return b;
    }
void stcpy(char *a,char *b,int i){
    int n=0,l=strlen(b);
    for(n=0;n<l&&n<i;n++){
        a[n]=b[n];
    }
    a[n]='';
}
int main(){
    char a[1000],b[3][10];
    scanf("%s",a);
    int i,k,k1,l=strlen(a),f=0;
    i=5;
    while(i>0){
        stcpy(b[0],a,i);
        stcpy(b[1],a+i,i);
        stcpy(b[2],a+i,i-1);
        int k[3]={n(b[0]),n(b[1]),n(b[2])};
        if(k[0]-k[1]==1||k[0]-k[1]==2||k[0]-k[2]==1||k[0]-k[2]==2){
            f=k[0];
            break;
        }
        i--;
    }
for(int i=0;i<l;i++){
    sprintf(b[0],"%d",f);
    if(strncmp(a+i,b[0],strlen(b[0]))==0)
    i+=strlen(b)-1;
    else{
        printf("%d",f);
        break;
    }
    f--;
}
}

This code is designed to find the missing number in a sequence of numbers that are arranged in descending order as a string. The input is a string of numbers, and the program needs to identify the missing number and print it as output. Let’s break down the code and create a simple algorithm to explain it:

Algorithm:

• Read the input string a.
• Define a function n to convert a substring to a long integer.
  • Initialize b to 0.
  • Loop through the characters of the string.
  • If the character is a digit, convert it to an integer and add it to b.
  • Return b as the converted integer.
• Define a function stcpy to copy the first i characters from string b to string a.
  • Initialize n to 0.
  • Loop until n reaches i or the end of b.
  • Copy each character from b to a.
  • Null-terminate a after copying.
• In the main function:
  • Define an array b to hold substrings of the input.
  • Read the input string a from the user.
  • Initialize variables i, k, k1, l, and f for loop control and storage.
  • Set i to 5, as we start looking for a missing number in a 5-digit sequence.
• Run a loop while i is greater than 0:
  • Use the stcpy function to split the input string into three substrings b[0], b[1], and b[2].
  • Convert these substrings to integers and store them in an array k.
  • Check if the difference between k[0] and k[1] is 1 or 2, or if the difference between k[0] and k[2] is 1 or 2.
  • If any of these conditions are met, set f to k[0] and break out of the loop.
  • If not, decrease i by 1 and continue the loop to check smaller sequences.
• Run a loop to compare the substrings of the input with the value of f.
  • Convert f to a string and store it in b[0].
  • Check if the substring of a starting from the current position matches b[0].
  • If it does, skip the length of b[0] characters in the input string.
  • If not, print f as the missing number and break out of the loop.
  • Decrease f by 1 to check for the next missing number.