題目連結：https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array
題目描述：
給定一個按照升序排列的整數陣列 nums，和一個目標值 target。找出給定目標值在陣列中的開始位置和結束位置。

如果陣列中不存在目標值 target，返回[-1, -1]。

進階：

你可以設計並實現時間複雜度為O(log n)的演算法解決此問題嗎？

示例 1：

輸入：nums = [5,7,7,8,8,10], target = 8
輸出：[3,4]
示例2：

輸入：nums = [5,7,7,8,8,10], target = 6
輸出：[-1,-1]
示例 3：

輸入：nums = [], target = 0
輸出：[-1,-1]

提示：

0 <= nums.length <= 105
-109<= nums[i]<= 109
nums是一個非遞減陣列
-109<= target<= 109

題解：

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int leftBoard = getLeftSearch(nums, target);
        int rightBoard = getRightSearch(nums, target);
        if(leftBoard <= rightBoard && nums[leftBoard] == target && nums[rightBoard] == target)
            return {leftBoard, rightBoard};
        return {-1, -1};
    }

    int getLeftSearch(vector<int>& nums, int target)
    {
        int left = -1;
        int right = nums.size();
        while(left + 1 != right)
        {
            int mid = left + (right - left) / 2;
            if(nums[mid] < target)
                left = mid;
            else
                right = mid;
        }
        return right;
    }

    int getRightSearch(vector<int>& nums, int target)
    {
        int left = -1;
        int right = nums.size();
        while(left + 1 != right)
        {
            int mid = left + (right - left) / 2;
            if(nums[mid] <= target)
                left = mid;
            else 
                right = mid;
            
        }
        return left;
    }
};