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Largest number with prime digits in C++
In this tutorial, we are going to write a program that finds the largest number with prime digits that is less than n.
Let's see the steps to solve the problem.
- Write a loop that iterates from 0 to n.
- If the current digit is not prime.
- While the digit is less 2, decrement the i value. If the i value is negative, then make it 0.
- Update the current index value with the next smallest prime digit.
- From the next index, make every digit to 7.
- If the current digit is not prime.
- Return n.
Example
Let's see the code.
#include <bits/stdc++.h>
using namespace std;
bool isPrime(char c) {
return c == '2' || c == '3' || c == '5' || c == '7';
}
void decrease(string& n, int i) {
if (n[i] <= '2') {
n.erase(i, 1);
n[i] = '7';
}else if (n[i] == '3') {
n[i] = '2';
}else if (n[i] <= '5') {
n[i] = '3';
}else if (n[i] <= '7') {
n[i] = '5';
}else {
n[i] = '7';
}
return;
}
string getPrimeDigitsNumber(string n) {
for (int i = 0; i < n.length(); i++) {
if (!isPrime(n[i])) {
while (n[i] <= '2' && i >= 0) {
i--;
}
if (i < 0) {
i = 0;
}
decrease(n, i);
for (int j = i + 1; j < n.length(); j++) {
n[j] = '7';
}
break;
}
}
return n;
}
int main() {
string n = "7464";
cout << getPrimeDigitsNumber(n) << endl;
return 0;
}Output
If you run the above code, then you will get the following result.
7377
Conclusion
If you have any queries in the tutorial, mention them in the comment section.
Updated on: 09-Apr-2021
319 Views
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