179. Largest Number Leetcode Java

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

Solution:

We need to build a new comparator with a comparison mechanism to sort the array to 9,5,34,3,30. The mechanism is to realize the largest number so if we have two numbers, for example, 30 and 34, there are two ways to form a number, 3034 and 3430, clearly 34 30 will be larger, similarly, using this mechanism, we can sort the array, 30<<3<<34<<5<<9, after we sort the array this way, we can easily find the largest number.

 public String largestNumber(int[] num) {  
     if(num==null || num.length==0) return "";  
     String[] temp=new String[num.length];  
     for(int i=0;i<num.length;i++){  
       temp[i]=String.valueOf(num[i]);  
     }  
     Comparator<String> myComparator=new Comparator<String>(){  
      @Override  
      public int compare(String a, String b){  
        String sa=a+b;  
        String sb=b+a;  
      return sb.compareTo(sa);  
      }  
     };  
     Arrays.sort(temp,myComparator);  
     if(temp[0].equals("0")) return "0";  
     StringBuilder sb=new StringBuilder();  
     for(int i=0;i<temp.length;i++){  
      sb.append(temp[i]);   
     }  
     return sb.toString();  
   }