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class Solution {
public:
    string convertIntToStr(int num)
    {
        char str[255];
        sprintf(str, "%d", num);
        return str;
    }

    vector<string> summaryRanges(vector<int>& nums) {
        vector<string> ranges;
        ranges.clear();
        if (nums.size() <= 0)
        {
            return ranges;
        }
        int start = nums[0];
        int end = nums[0];
        for (int i = 1;i < nums.size(); i++)
        {
            if (nums[i] - nums[i-1] == 1)
            {
                end = nums[i];
            }
            else
            {
                string item = convertIntToStr(start);
                if (end == start)
                {
                    ranges.push_back(item);
                }
                else
                {
                    item += "-";
                    item += convertIntToStr(end);
                    ranges.push_back(item);
                }
                start = nums[i];
                end = start;
            }
        }
        string item = convertIntToStr(start);
        if (end == start)
        {
            ranges.push_back(item);
        }
        else
        {
            item += "-";
            item += convertIntToStr(end);
            ranges.push_back(item);
        }
        return ranges;
    }
};