Leetcode 2384 Largest Palindromic Number Solution in Java | Hindi Coding Community

 

You are given a string num consisting of digits only.

Return the largest palindromic integer (in the form of a string) that can be formed using digits taken from num. It should not contain leading zeroes.

Notes:

• You do not need to use all the digits of num, but you must use at least one digit.
• The digits can be reordered.

 

Example 1:

Input: num = "444947137"
Output: "7449447"
Explanation: 
Use the digits "4449477" from "444947137" to form the palindromic integer "7449447".
It can be shown that "7449447" is the largest palindromic integer that can be formed.

Example 2:

Input: num = "00009"
Output: "9"
Explanation: 
It can be shown that "9" is the largest palindromic integer that can be formed.
Note that the integer returned should not contain leading zeroes.

 

Constraints:

• 1 <= num.length <= 105
• num consists of digits.

Java Code :

public String largestPalindromic(String num) {

HashMap<Integer,Integer> hm = new HashMap<>();

for(int i=0;i<num.length();i++){

int value = num.charAt(i) - '0';

hm.put(value,hm.getOrDefault(value,0)+1);

}

StringBuilder sb = new StringBuilder();

StringBuilder rev = new StringBuilder();

while(true){

boolean flag = false;

for(int i=9;i>=0;i--){

if(sb.length() == 0 && i == 0) continue;

int freq = hm.getOrDefault(i,0);

if(freq != 0){

if(freq%2 == 0){

for(int j=1;j<=freq/2;j++){

sb.append(i);

rev.append(i);

flag = true;

}

hm.put(i,0);

}

else{

int value = freq/2;

int mod = freq%2;

for(int j=1;j<=value;j++){

sb.append(i);

rev.append(i);

flag = true;

}

hm.put(i,mod);

}

}

}

if(!flag) break;

}

for(int i=9;i>=0;i--){

if(hm.containsKey(i) && hm.get(i)>0){

sb.append(i);

break;

}

}

String str = (sb.toString() + rev.reverse().toString());

return str;

}