思路：先二分查找到一个和target相同的元素，然后再左边二分查找左边界，右边二分查找有边界。
class Solution {
public:
int begin = -, end = -;
int ends;
int lSearch(int left, int right, vector<int>& nums, int target)
{
if(left > right) return -;
int mid = (left + right) / ;
if(nums[mid] == target){
if(mid == || (mid > && nums[mid - ] < target)) return mid;
else return lSearch(left,mid - ,nums,target);
}else
return lSearch(mid + ,right,nums,target);
return -;
}
int rSearch(int left, int right, vector<int>& nums, int target)
{
if(left > right) return -;
int mid = (left + right) / ;
if(nums[mid] == target){
if(mid == ends || (mid < ends && nums[mid + ] > target)) return mid;
else return rSearch(mid + ,right,nums,target);
}else
return rSearch(left ,mid - ,nums,target);
return -;
}
int midSearch(int left, int right, vector<int>& nums, int target)
{
if(left > right) return -;
int mid = (left + right) / ;
if(nums[mid] == target){
return mid;
}
else if(nums[mid] < target) return midSearch(mid + ,right,nums,target);
else if(nums[mid] > target) return midSearch(left, mid - ,nums,target);
return -;
}
vector<int> searchRange(vector<int>& nums, int target) {
ends = nums.size() - ;
int mid = midSearch(,ends,nums,target);
if(mid != -){
begin = lSearch(,mid,nums,target);
end = rSearch(mid,ends,nums,target);
}
vector<int> ans;
ans.push_back(begin);
ans.push_back(end);
return ans;
}
};