179. Largest Number

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class Solution {
    public String largestNumber(int[] nums) {
        String[] numStrArray = new String[nums.length];
        for (int i = 0; i < nums.length; i++) {
            numStrArray[i] = String.valueOf(nums[i]);
        }

        Arrays.sort(numStrArray, (o1, o2) -> (o2 + o1).compareTo(o1 + o2));
        String res = String.join("", numStrArray);

        // 注意处理多个前导 0 的情况，如 nums: [0, 0]
        int firstNonZeroIndex = 0;
        while (firstNonZeroIndex < res.length() - 1 && res.charAt(firstNonZeroIndex) == '0') {
            firstNonZeroIndex++;
        }
        return res.substring(firstNonZeroIndex);
    }
}

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class Solution {
    public String largestNumber(int[] nums) {
        List<Integer> numList = new ArrayList<>(nums.length);
        for (int num : nums) {
            numList.add(num);
        }

        numList.sort((x, y) -> {
            // xy > yx
            long product = 10;
            while (product <= y) {
                product *= 10;
            }
            long a = x * product + y;

            product = 10;
            while (product <= x) {
                product *= 10;
            }
            long b = y * product + x;

            return a == b ? 0 : (a - b > 0 ? -1 : 1); // 注意此处的顺序
        });

        StringBuilder sb = new StringBuilder();
        for (int num : numList) {
            sb.append(num);
        }
        String res = sb.toString();

        // 注意处理多个前导 0 的情况，如 nums: [0, 0]
        int firstNonZeroIndex = 0;
        while (firstNonZeroIndex < res.length() - 1 && res.charAt(firstNonZeroIndex) == '0') {
            firstNonZeroIndex++;
        }
        return res.substring(firstNonZeroIndex);
    }
}

References

179. Largest Number