每次思考都是一次进步 

1、如果要求时间复杂度为O(logn)，那么很大可能

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int thesize=nums.size();
        vector<int> q(2,-1);
        if(thesize==0)return  q; 
        int l=0,r=thesize-1,mid;
        double t1=target-0.5;
        double t2=target+0.5;
        while(l<r)
        {
            mid=l+(r-l)/2;
            if(nums[mid]<t1) l=mid+1;
            else r=mid;         
        }
        if(nums[l]!=target) return q;
        else q[0]=l;
        l=0,r=thesize-1;
        while(l<r)
        {
            mid=l+(r-l+1)/2;
            if(nums[mid]<t2) l=mid;
            else r=mid-1;
        }
        q[1]=l;
        return q;
    }
};