179. Largest Number

the key is this:

        Arrays.sort(str, (String s1, String s2) -> (s2+s1).compareTo(s1+s2));

sort input [3,30,34,5,9]

to [9, 5, 34, 3, 30]

ex: 34,3 -> 334, 343 compare which one is bigger

need to handle edge case for all zero : ["0", "0", "0"]

class Solution {
    public String largestNumber(int[] nums) {
        List<String> list = new ArrayList<>();
        for (int num : nums) {
            list.add(String.valueOf(num));
        }
        Collections.sort(list, (a, b) -> (b + a).compareTo(a + b));
        // for "0", "0", "0" case
        if (!list.isEmpty() && list.get(0).length() > 0 && list.get(0).charAt(0) == '0') {
            return "0";
        }
        StringBuilder result = new StringBuilder();
        for (String s : list) {
            result.append(s);
        }
        return result.toString();
    }
}

/**
compare first digits on the left first
if first digits is the same but len is different


330
303

32 30 3

33230

32330
32303

45 41 4

44341

45441

443 43 4

443434
444343


30 3

303 330

using a+b comapre to b+a!
 */

Time: O(nlogn)

space: O(n)

class Solution {
    public String largestNumber(int[] nums) {
        String str[] = new String[nums.length];
        for (int i = 0; i < nums.length ; i++) {
            str[i] = String.valueOf(nums[i]);
        }
        
        Arrays.sort(str, (String s1, String s2) -> (s2+s1).compareTo(s1+s2));
        
        if (str[0].charAt(0) == '0') return "0"; //corner case
        
        StringBuilder sb = new StringBuilder();
        for (String s : str) {
            sb.append(s);
        }
        return sb.toString();
    }
}

```java
class Solution {
    public String largestNumber(int[] nums) {
        String[] str = new String[nums.length];
        for (int i = 0; i < nums.length; i++) {
            str[i] = String.valueOf(nums[i]);
        }
        Arrays.sort(str, (a, b) -> (b+a).compareTo(a+b));
        // so large one will in front of it
        // so if the first one is 0, result is 0
        // if (str[0].length() > 0 && str[0].charAt(0) == '0') {
        //     return "0";
        // }

        StringBuilder sb = new StringBuilder();
        for (String s : str) {
            sb.append(s);
        }
        return sb.charAt(0) == '0' ? "0" : sb.toString(); // or just check first one char is 0 or not
    }
}
```