179. Largest Number

LeetCode

To get a largest number, we can convert the numbers to strings and sort these strings in descending order. But when two strings have the same beginning, here comes a problem. For example, "30" and "3" have the same beginning, when we sort them in descending order, the concatenation of "30" + "3" is "303", which is smaller than "3" + "30" = "330".

Thus when we customized a comparator, it won’t follow the simple descending order but compares two of the concatenations of the strings.

class Solution {
    public String largestNumber(int[] nums) {
        String[] numStrs = new String[nums.length];
        for (int i = 0; i < nums.length; i++) {
            numStrs[i] = String.valueOf(nums[i]);
        }
        Arrays.sort(numStrs, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                String order1 = o1 + o2;
                String order2 = o2 + o1;
                return order2.compareTo(order1);
            }
        });
        if (numStrs[0].charAt(0) == '0') {
            return "0";
        }
        StringBuilder builder = new StringBuilder();
        for (String str : numStrs) {
            builder.append(str);
        }
        return builder.toString();
    }
}