public class Solution
{
    public void NextPermutation(int[] nums)
    {
        var i = nums.Length - 2;
        while(i >= 0 && nums[i] >= nums[i+1])
            i--;
        if(i >= 0)
        {
            var j = nums.Length - 1;
            while(nums[i] >= nums[j])
                j--;
            (nums[i], nums[j]) = (nums[j], nums[i]);
        }
        Array.Reverse(nums, i+1, nums.Length-i-1);
    }
}