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class Solution {
public:
    void nextPermutation(vector<int>& nums) {
        if (nums.empty() || nums.size() == 0) return;
        
        int firstSmall = -1;
        for (int i = nums.size() - 2; i >= 0; i--) {
            if (nums[i] < nums[i + 1]) {
                firstSmall = i;
                break;
            }
        }
        
        if (firstSmall == -1) {
            reverse(nums.begin(), nums.end());
            return;
        }
        
        int firstLarge = -1;
        for (int i = nums.size() - 1; i > firstSmall; i--) {
            if (nums[i] > nums[firstSmall]) {
                firstLarge = i;
                break;
            }
        }
        
        swap(nums[firstSmall], nums[firstLarge]);
        reverse(nums.begin() + firstSmall + 1, nums.end());   // need "+1"
        return;
    }
};