556. Next Greater Element III

class Solution {
    public int nextGreaterElement(int n) {
        if (n < 10) {
            return -1;
        }

        char[] chars = String.valueOf(n).toCharArray();

        int lowerIndex = -1;
        for (int i = chars.length - 1; i > 0; i--) {
            if (chars[i - 1] < chars[i]) {
                lowerIndex = i - 1;
                break;
            }
        }

        if (lowerIndex != -1) {
            for (int i = chars.length - 1; i > lowerIndex; i--) {
                if (chars[i] > chars[lowerIndex]) {
                    swap(chars, i, lowerIndex);
                    reverse(chars, lowerIndex + 1, chars.length - 1);
                    break;
                }
            }
        } else {
            return -1;
        }

        int res = 0;
        for (char c : chars) {
            int num = c - '0';
            if (res > Integer.MAX_VALUE / 10 || (res == Integer.MAX_VALUE / 10 && num > 7)) {
                return -1;
            } else {
                res = res * 10 + num;
            }
        }

        return res;
    }

    private void reverse(char[] chars, int i, int j) {
        while (i < j) {
            swap(chars, i++, j--);
        }
    }

    private void swap(char[] chars, int i, int j) {
        char tmp = chars[i];
        chars[i] = chars[j];
        chars[j] = tmp;
    }
}
Reference
