Largest even number that can be formed by any number of swaps
Last Updated :
15 Dec, 2022
Given an integer N in the form of string, the task is to find the largest even number from the given number when you are allowed to do any number of swaps (swapping the digits of the number). If no even number can be formed then print -1.
Examples:
Input: N = 1324
Output: 4312
Input: N = 135
Output: -1
No even number can be formed using odd digits.
Approach: Sort the string in descending order then we will get the largest number possible with the given digit but it may or may not be an even number. In order to make it even (if it not already), an even digit from the number must be swapped with the last digit and in order to maximize the even number, the even digit which is to be swapped must the smallest even digit from the number.
Note that the sorting can be done in linear time using frequency array for the digits of the number as the number of distinct elements that are needed to be sorted can be at most 10 in the worst case.
Below is the implementation of the above approach:
C++
#include <bits/stdc++.h>
using namespace std;
const int MAX = 10;
string getMaxEven(string str, int len)
{
int freq[MAX] = { 0 };
int i, minEvenDigit = MAX;
for (i = 0; i < len; i++) {
int digit = str[i] - '0' ;
freq[digit]++;
if (digit % 2 == 0)
minEvenDigit = min(digit, minEvenDigit);
}
if (minEvenDigit == MAX)
return "-1" ;
freq[minEvenDigit]--;
i = 0;
for ( int j = MAX - 1; j >= 0; j--) {
for ( int k = 0; k < freq[j]; k++)
str[i++] = ( char )(j + '0' );
}
str[i] = ( char )(minEvenDigit + '0' );
return str;
}
int main()
{
string str = "1023422" ;
int len = str.length();
cout << getMaxEven(str, len);
return 0;
}
|
Java
import java.io.*;
public class GFG {
static int MAX = 10 ;
static String getMaxEven(String str, int len)
{
String maxEven= "" ;
int [] freq = new int [MAX];
int i, minEvenDigit = MAX;
for (i = 0 ; i < len; i++) {
int digit = str.charAt(i) - '0' ;
freq[digit]++;
if (digit % 2 == 0 )
minEvenDigit
= Math.min(digit, minEvenDigit);
}
if (minEvenDigit == MAX)
return "-1" ;
freq[minEvenDigit]--;
i = MAX- 1 ;
while (i>= 0 )
{
if (freq[i]> 0 )
{
maxEven= maxEven+i;
freq[i]--;
} else
i--;
}
maxEven= maxEven+minEvenDigit;
return maxEven;
}
public static void main(String[] args)
{
String str = "1023422" ;
int len = str.length();
System.out.println(getMaxEven(str, len));
}
}
|
Python3
MAX = 10
def getMaxEven(string, length):
string = list (string)
freq = [ 0 ] * MAX
minEvenDigit = MAX
minDigit = MAX
for i in range (length):
digit = ord (string[i]) - ord ( '0' )
freq[digit] + = 1
if (digit % 2 = = 0 ):
minEvenDigit = min (digit, minEvenDigit)
minDigit = min (digit, minDigit)
if (minEvenDigit = = MAX ):
return "-1"
freq[minEvenDigit] - = 1
freq[minDigit] - = 1
i = 0
for j in range ( MAX - 1 , - 1 , - 1 ):
for k in range (freq[j]):
string[i] = chr (j + ord ( '0' ))
i + = 1
if (j = = minEvenDigit):
string[i] = chr (minDigit + ord ( '0' ))
i + = 1
string[ - 1 ] = chr (minEvenDigit + ord ( '0' ))
return "".join(string)
if __name__ = = "__main__" :
string = "1023422"
length = len (string)
print (getMaxEven(string, length))
|
C#
using System;
class GFG {
static int MAX = 10;
static String getMaxEven( char [] str, int len)
{
int [] freq = new int [MAX];
int i, minEvenDigit = MAX, minDigit = MAX;
for (i = 0; i < len; i++) {
int digit = str[i] - '0' ;
freq[digit]++;
if (digit % 2 == 0)
minEvenDigit
= Math.Min(digit, minEvenDigit);
minDigit = Math.Min(digit, minDigit);
}
if (minEvenDigit == MAX)
return "-1" ;
freq[minEvenDigit]--;
freq[minDigit]--;
i = 0;
for ( int j = MAX - 1; j >= 0; j--) {
for ( int k = 0; k < freq[j]; k++)
str[i++] = ( char )(j + '0' );
if (j == minEvenDigit)
str[i++] = ( char )(minDigit + '0' );
}
str[i - 1] = ( char )(minEvenDigit + '0' );
return String.Join( "" , str);
}
public static void Main(String[] args)
{
char [] str = "1023422" .ToCharArray();
int len = str.Length;
Console.WriteLine(getMaxEven(str, len));
}
}
|
Javascript
<script>
let MAX = 10;
function getMaxEven(str, len)
{
let freq = new Array(MAX);
freq.fill(0);
let i, minEvenDigit = MAX, minDigit = MAX;
for (i = 0; i < len; i++) {
let digit = str[i].charCodeAt() - '0' .charCodeAt();
freq[digit]++;
if (digit % 2 == 0)
minEvenDigit
= Math.min(digit, minEvenDigit);
minDigit = Math.min(digit, minDigit);
}
if (minEvenDigit == MAX)
return "-1" ;
freq[minEvenDigit]--;
freq[minDigit]--;
i = 0;
for (let j = MAX - 1; j >= 0; j--) {
for (let k = 0; k < freq[j]; k++)
str[i++] = String.fromCharCode(j + '0' .charCodeAt());
if (j == minEvenDigit)
str[i++] = String.fromCharCode(minDigit + '0' .charCodeAt());
}
str[i - 1] = String.fromCharCode(minEvenDigit + '0' .charCodeAt());
return str.join( "" );
}
let str = "1023422" .split( '' );
let len = str.length;
document.write(getMaxEven(str, len));
</script>
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Time Complexity: O(n + MAX)
Auxiliary Space: O(MAX)
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