34 find the first and last position of elements in a sorted array

34. 在排序数组中查找元素的第一个和最后一个位置

cpp：

正确代码：

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target)
    {
        int Left = findLeftBoundary(nums, target);
        int Right = findRightBoundary(nums, target);
        
        if (Left == -1 || Right == -1)
        {
            return {-1, -1};
        }

        return {Left, Right};
    }

private:
    int findLeftBoundary(vector<int>& nums, int target)
    {
        int left = 0;
        int right = nums.size() - 1;
        int leftBoundary = -1; //给边界赋初始值便于标识

        while (left <= right)
        {
            int middle = left + (right - left) / 2; //防止越界
            if (nums[middle] < target)
            {
                left  = middle + 1;
            }
            else //即left >= target
            {
                if (nums[middle] == target)
                {
                    leftBoundary = middle;
                }
                right = middle - 1;
            }
        }

        return leftBoundary;
    }

    int findRightBoundary(vector<int>& nums, int target)
    {
        int left = 0;
        int right = nums.size() - 1;
        int rightBoundary = -1;

        while (left <= right)
        {
            int middle = left + (right - left) / 2;
            if (nums[middle] > target)
            {
                right = middle - 1;
            }
            else
            {
                if (nums[middle] == target)
                {
                    rightBoundary = middle;
                }
                left = middle + 1;
            }
        }

        return rightBoundary;
    }
};

错误代码：

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target)
    {
        int left_find_leftBoundary = 0;
        int left_find_rightBoundary = 0;
        int right_find_leftBoundary = nums.size() - 1;
        int right_find_rightBoundary = nums.size() - 1;
        int leftBoundary = 0;
        int rightBoundary = 0;

        while (left_find_leftBoundary <= right_find_leftBoundary && left_find_rightBoundary <= right_find_rightBoundary)
        {
            while (left_find_leftBoundary <= right_find_leftBoundary)
            {
                int middle_find_leftBoundary = left_find_leftBoundary + (right_find_leftBoundary - left_find_leftBoundary) / 2;
                if (nums[middle_find_leftBoundary] > target)
                {
                    right_find_leftBoundary = middle_find_leftBoundary - 1;
                }
                else if (nums[middle_find_leftBoundary] < target)
                {
                    left_find_leftBoundary = middle_find_leftBoundary + 1;
                }
                else if (nums[middle_find_leftBoundary == target])
                {
                    leftBoundary = middle_find_leftBoundary;
                    break;
                }
                else
                {
                    leftBoundary = left_find_leftBoundary;
                    break;
                }
            }

            while (left_find_rightBoundary <= right_find_rightBoundary)
            {
                int middle_find_rightBoundary = left_find_rightBoundary + (right_find_rightBoundary - left_find_rightBoundary) / 2;
                if (nums[middle_find_rightBoundary] > target)
                {
                    right_find_rightBoundary = middle_find_rightBoundary - 1;
                }
                else if (nums[middle_find_rightBoundary] < target)
                {
                    left_find_rightBoundary = middle_find_rightBoundary + 1;
                }
                else if (nums[middle_find_rightBoundary == target])
                {
                    rightBoundary = middle_find_rightBoundary;
                    break;
                }
                else
                {
                    rightBoundary = left_find_rightBoundary;
                    break;
                }
            }

            return {leftBoundary, rightBoundary};
        }

        return {-1, -1};
    }
};