34. 在排序数组中查找元素的第1个和最后1个位置

显然是二分，关键在于怎么处理mid，+1，-1的微妙处。

cpp实现：

#include
#include
using namespace std;

// @lc code=start
class Solution {
public:
    vector searchRange(vector& nums, int target) {
        if (nums.size()==0){
            return vector {-1,-1};
        }
        int low = lowerFound(nums,target);
        int high = upperFound(nums,target);
        if (low<0 || low>=nums.size()){
            // 越界
            low = -1;
        }// 值不相等
        else if  (nums[low]!=target) low=-1;

        if (high<0 || high>=nums.size()){
            // 越界
            high = -1;
        }
        // 值不相等        
        else if (nums[high]!=target) high=-1;

        return vector {low,high};
    }
    int lowerFound(vector& nums, int target){
        int left=0, right=nums.size()-1;        
        while(lefttarget){
                // 在左边
                right = mid-1;
            }
        }
        cout<<"left: "< nums, int target){
        int left=0, right=nums.size()-1;        
        while(lefttarget){
                // 在左边
                right = mid-1;
            }
        }
        if (nums[left]==target){
            // 如果是[7,7,7],7这种情况
            return left;
        }
        cout<<"high: "<