Leetcode 556. Next Greater Element III

Given a positive 32-bit integer n, you need to find the smallest 32-bit integer which has exactly the same digits existing in the integer nand is greater in value than n. If no such positive 32-bit integer exists, you need to return -1.

Example 1:

Input: 12
Output: 21

Example 2:

Input: 21
Output: -1

Code (Java):

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class Solution {     public int nextGreaterElement(int n) {         String s = n + "";         char[] arr = s.toCharArray();           // step 1: go from end and find the descreasing number         //         int i = s.length() - 2;         while (i >= 0 && s.charAt(i) >= s.charAt(i + 1)) {             i--;         }           if (i < 0) {             return -1;         }           int j = i + 1;         while (j < s.length() && s.charAt(j) > s.charAt(i)) {             j++;         }         j--;           swap(arr, i, j);           reverse(arr, i + 1);           String ans = new String(arr);                   Long l = Long.parseLong(ans);         if (l >= Integer.MAX_VALUE) {             return -1;         }           return Integer.parseInt(ans);     }       private void swap(char[] arr, int i, int j) {         char temp = arr[i];         arr[i] = arr[j];         arr[j] = temp;       }       private void reverse(char[] arr, int start) {         int end = arr.length - 1;           while (start < end) {             swap(arr, start, end);             start++;             end--;         }     } }