LeetCode|Summary Ranges

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Summary Ranges

Given a sorted integer array without duplicates, return the summary of its ranges.

For example, given [0,1,2,4,5,7], return [“0->2”,”4->5”,”7”].

注意：有INT_MAX和INT_MIN，减法小心溢出，还有-INT_MIN也会溢出

class Solution {
public:
    vector<string> summaryRanges(vector<int>& nums) {
        vector<string> res;
        int len = nums.size(), cnt = 1;
        if(len == 0) return res;
        string str = int2str(nums[0]);
        nums.push_back(nums[len-1] + 2); // add a termiator, abs(diff) = 2
        for(int i = 1; i <= len; i++){
            if( (long long)nums[i]-nums[i-1] == 1) {
                cnt++;
            } else {
                if(cnt == 1) res.push_back(str);
                else res.push_back(str + "->" + int2str(nums[i-1]));
                cnt = 1;
                str = int2str(nums[i]);
            }
        } return res;
    }
private:
    string int2str(long long x){
        if(x == 0) return "0";
        bool isNeg = (x < 0);
        if(x < 0) x = -x;
        stack<char> s;
        while(x != 0){
            s.push(x%10+'0');
            x /= 10;
        }
        string res;
        if(isNeg) res = "-";
        while(!s.empty()){
            res += s.top();
            s.pop();
        } return res;
    }
};