556. next larger element iii- (31. next permutation) - two iterations

One 、 Title Description

Give you a positive integer n , Please find the smallest integer that meets the conditions , It consists of rearranging n Each number present in the consists of , And its value is greater than n . If there is no such positive integer , Then return to -1 .

Be careful , The returned integer should be a 32 An integer , If there is an answer that satisfies the meaning of the question , But it's not 32 An integer , Also return to -1 .

Example 1：

 Input ：n = 12
 Output ：21

Example 2：

 Input ：n = 21
 Output ：-1

Two 、 Problem solving

Two traversal

This question is similar to 31 Next arrangement , But what appears here is to give a positive integer ,31 The question is an array , So you need to change a positive integer into a character array .

public class Solution {
    
    public int nextGreaterElement(int n) {
    
        // Convert numbers to character arrays 
        char[] nums = ("" + n).toCharArray();
        int length = nums.length;
        int end = length - 2;
        // If the current value is greater than the following value , Keep looking for , Always find the first ascending subscript 
        while(end >= 0 && nums[end] >= nums[end+1]){
    
            end--;
        } 
        // Pay attention to the boundary conditions 
        if(end < 0){
    
            return -1;
        }

        // After finding the subscript value , Find a value greater than the subscript value after 
       
        if(end >= 0){
    
            int next = length - 1;
            while(next >= 0 && nums[end] >= nums[next]){
    
                next--;
            }
            swap(nums,end,next);
        }

        // Flip 
        reverse(nums,end+1);
        // To prevent cross-border 
        try {
    
            return Integer.parseInt(new String(nums));
        } catch (Exception e) {
    
            return -1;
        }
    }
    // Flip array 
    public void reverse(char[] nums,int left){
    
        int right = nums.length-1;
        while(left <= right){
    
            swap(nums,left,right);
            left++;
            right--;
        }
    }
    // Swap arrays 
    public void swap(char[] nums,int left,int right){
    
        char temp = nums[left];
        nums[left] = nums[right];
        nums[right] = temp;
    }
}