Next Palindrome Using Same Digits

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Problem Description

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Solutions

Solution 1: C# (Best: 157 ms)

Metric	Value
Runtime	157 ms
Memory	40.5 MB
Date	2022-01-19

Solution

public class Solution {
    public string NextPalindrome(string num) {
        int len = num.Length;
    char[] result = new char[len];
    int mid = len/2;
    int[] arr = new int[mid];
    for (int i = 0; i < mid; i++)
    {
        arr[i] = (int)(num[i] - '0');
    }

    int pivot = -1;
    for (int i = mid - 1; i > 0; i--)
    {
        if (arr[i - 1] < arr[i])
        {
            pivot = i - 1;
            break;
        }
    }
    if (pivot == -1) return "";
    else
    {
        int index = -1;
        for (int i = mid - 1; i >= pivot; i--)
        {
            if (arr[i] > arr[pivot])
            {
                index = i;
                break;
            }
        }
        Swap(arr, pivot, index);
        Array.Reverse(arr, pivot + 1, mid - pivot - 1);
    }
    
    for (int i = 0, j =len-1; i < j; i++, j--)
    {
        result[i] = (char)(arr[i]+'0');
        result[j] = (char)(arr[i]+'0');
    }
    if(len%2 == 1) result[len/2] = num[len/2];
    return new string(result);
        }

private void Swap(int[] arr, int i , int j)
{
    int temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}
}

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Complexity Analysis

Approach	Time	Space
Solution	To be analyzed	To be analyzed