重点

只需要记住两点：
1.left = right 时，一定就是最终结果（包括找不到目标值），无需再次判断，如果判断就会死循环
2.求中点如果是求左端点 mid = left + (right - left)/2
如果是求右端点 mid = left + (right - left + 1)/2
简称（右加一）

class Solution {
public:vector<int> searchRange(vector<int>& nums, int target) {if(nums.size() == 0) return {-1, -1};int left = 0;int right = nums.size()-1;//寻找左点端int begin = 0;while(left < right){int mid = left + (right - left)/2;if(nums[mid] < target) left = mid+1;else if(nums[mid] >= target) right = mid;}if(nums[left] != target) return {-1, -1};else begin = left;//寻找右端点left = 0;right = nums.size()-1;while(left < right){int mid = left + (right-left+1)/2;if(nums[mid]<=target) left = mid;else right = mid-1; }return {begin,right};}
};