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Next higher number using atmost one swap operation in C++
Given a number n, swap any two digits of the number so that the resulting number is greater than the number n. If it's not possible then print -1. Let's see an example.
Input
12345
Output
12354
We have swapped the digits 4 and 5. And we got the higher number with one swap.
Algorithm
It's not possible to form the number if the digits of the number are in decreasing order.
Find the index of the digit from the right of the number which is less than the last digit.
Find the index of the digit which is greater than the previous digit and less than all digits.
Swap two digits and return the new number.
- Return the new number.
Implementation
Following is the implementation of the above algorithm in C++
#include <bits/stdc++.h>
using namespace std;
string getNextHigherNumber(string num) {
int len = num.size();
int firstDigitIndex = -1;
for (int i = len - 2; i >= 0; i--) {
if (num[i] < num[len - 1]) {
firstDigitIndex = i;
break;
}
}
if (firstDigitIndex == -1) {
return "-1";
}
int secondDigitIndex = -1;
for (int i = len - 1; i > firstDigitIndex; i--) {
if (num[i] > num[firstDigitIndex]) {
if (secondDigitIndex == -1 || num[i] <= num[secondDigitIndex]) {
secondDigitIndex = i;
}
}
}
char temp = num[firstDigitIndex];
num[firstDigitIndex] = num[secondDigitIndex];
num[secondDigitIndex] = temp;
return num;
}
int main() {
string num = "12345";
cout << "Given number: " << num << endl;
cout << "Next higher number: " << getNextHigherNumber(num) << endl;
return 0;
}Output
If you run the above code, then you will get the following result.
Given number: 12345 Next higher number: 12354
Updated on: 25-Oct-2021
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