LeetCode之Summary Ranges

class Solution {
public:
    vector<string> summaryRanges(vector<int>& nums) {
        vector<string> res;
        if(nums.empty()) return res;
        int first(0);
        for(int i = 0; i < nums.size(); ++i){
            if(i == nums.size()-1 || nums[i+1] > nums[i] + 1){//出现新的子段
                string tmp_res;
                tmp_res += num2string(nums[first]);
                if(i > first){
                   tmp_res += "->";
                   tmp_res += num2string(nums[i]);
                }
                res.push_back(tmp_res);
                first = i+1;
            }
        }
        return res;
    }
    
    string num2string(int num){
        stringstream s;
        string line;
        s << num;
        s >> line;
        return line; 
    }
};