Maximum number [abstract rules for abstract sorting]

Preface

The most difficult problem is just a combination of several small problems , But there are two difficult questions , It's a math problem / Abstract problem . Such as abstract dichotomy / Abstract sort .
This article uses the maximum number to practice abstract sorting and abstract sorting rules .

One 、 The maximum number

Two 、 Abstract rules

package everyday.medium;

import java.util.ArrayList;
import java.util.List;

//  The maximum number 
public class LargestNumber {
    
    /* target： Splice the numbers , Look who's big .  Is to put the numbers in order , But it should be arranged according to the rules of string comparison ( The rules ： Who splices the string before is bigger .), So even if the abstract sort , Abstract sorting rules . */
    public String largestNumber(int[] nums) {
    
        //todo  Abstract rules , Sort by yourself , other sort
        List<Integer> arr = new ArrayList<>();
        //  Wrap the elements into Integer, Can be transmitted to the comparator .
        for (int num : nums) arr.add(num);
        //  Compare ： Define your own comparison rules .
        arr.sort((o1, o2) -> new StringBuilder().append(o2).append(o1).
                compareTo(new StringBuilder().append(o1).append(o2)));
        //  Get the concatenated string of numbers .
        StringBuilder sb = new StringBuilder();
        for (Integer val : arr) sb.append(val);
        // bug1: When all are 0 when , The leading will appear as 0
        // return sb.toString();
        return sb.charAt(0) == '0' ? "0" : sb.toString();
    }
}

summary

1） Abstract sort

reference

[1] LeetCode The maximum number