Given a non-negative integer, you could swap two digits at most once to get the maximum valued number. Return the maximum valued number you could get.

Example 1:

Input: 2736
Output: 7236
Explanation: Swap the number 2 and the number 7.

Example 2:

Input: 9973
Output: 9973
Explanation: No swap.

Note:

1. The given number is in the range [0, 108]

 1 public class Solution {
 2     public int MaximumSwap(int num) {
 3         if (num < 10) return num;
 4         
 5         var list = new List<int>(32);
 6         
 7         int tmp = num;
 8         while (tmp > 0)
 9         {
 
10             list.Insert(0, tmp % 10);
11             tmp /= 10;
12         }
13         
14         var maxRight = new int[list.Count];
15         var max = list[list.Count - 1];
16         
17         for (int i = maxRight.Length - 1; i >= 0; i--)
18         {
19             maxRight[i] = Math.Max(list[i], max);
 
20             max = maxRight[i];
21         }
22         
23         for (int i = 0; i < list.Count; i++)
24         {
25             if (list[i] < maxRight[i])
26             {
27                 for (int j = list.Count - 1; j >= 0; j--)
28                 {
29                     if (list[j] == maxRight[i])
30                     {
31                         list[j] = list[i];
32                         list[i] = maxRight[i];
33                         
34                         return CreateInt(list);
35                     }
36                 }
37             }
38         }
39         
40         return num;
41     }
42     
43     private int CreateInt(IList<int> list)
44     {
45         int result = 0;
46         
47         for (int i = 0; i < list.Count; i++)
48         {
49             result = result * 10 + list[i];
50         }
51         
52         return result;
53     }
54 }

Leetcode 670: Maximum Swap