class Solution {
    public void nextPermutation(int[] nums) {
        int i = nums.length - 2;
        while (i >= 0 && nums[i] >= nums[i + 1]){
            i--;
        }

        if (i >= 0){
            int j = nums.length - 1;
            while (j > 0 && nums[j] <= nums[i]){
                j--;
            }
            swap(nums, i, j);    
        }

        reverse(nums, i + 1);
    }

    private void swap(int[] nums, int i, int j){
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }

    private void reverse(int[] nums, int start){
        int end = nums.length - 1;
        while (start < end){
            int temp = nums[start];
            nums[start] = nums[end];
            nums[end] = temp;

            start++;
            end--;
        }
    }
}