Question

How to check if number can be made prime by deleting a single digit in C

Answer 1

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

unsigned int remove_N_digit(unsigned int n, const int index_from, const int index_to) {
    static char tmp[10];
     
    sprintf(tmp, "%d", n);

    int sectionlen = index_to - index_from;
    int stringlen = strlen(tmp);

    memmove(tmp + index_from, tmp + index_from + sectionlen, stringlen - index_to);
    tmp[stringlen - sectionlen] = '\0';

    return atoi(tmp);
}

bool isPrime(int n) {
    if (n == 0) return false;
    if (n == 1) return false;
   
    for (int i = 2; i <= sqrt(n); i++) {
        if (n % i == 0) {
            return false;
        }
    }
     
    return true;
}
 
int main(void) {
    unsigned int n = 78919;
    unsigned int total_digits = (int)log10(n) + 1;

    int i = 0;
    while (i < total_digits) {
        int tmp = remove_N_digit(n, i, i + 1);
        if (isPrime(tmp)) {
            printf("yes number = %d\n", tmp);
            break;
        }
        i++;
    }
     
    return 0;
}
 
 
   
/*
run:
   
yes number = 7919

*/

 

 

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