LeetCode 34 - Search for a Range

Search for a Range

Given a sorted array of integers, find the starting and ending position of a given target value.

Your algorithm's runtime complexity must be in the order of O(log n).

If the target is not found in the array, return 

[-1, -1]

.

For example,

Given 

[5, 7, 7, 8, 8, 10]

 and target value 8,

return 

[3, 4]

.

My Code

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int size = nums.size();
        int left_idx = 0;
        int right_idx = size - 1;
        int mid_idx;
        vector<int> range(2, -1);

        // Find start
        while (left_idx <= right_idx)
        {
            mid_idx = (left_idx + right_idx) / 2;
            if (nums[mid_idx] == target)
            {
                if (mid_idx == 0 || nums[mid_idx-1] < target)
                {
                    range[0] = mid_idx;
                    break;
                }
                else
                    right_idx = mid_idx - 1;
            }
            else if (nums[mid_idx] < target)
                left_idx = mid_idx + 1;
            else
                right_idx = mid_idx - 1;
        }

        // Find end
        if (range[0] != -1)
        {
            left_idx = range[0] + 1;
            right_idx = size - 1;

            while (left_idx <= right_idx)
            {
                mid_idx = (left_idx + right_idx) / 2;
                if (nums[mid_idx] == target)
                {
                    if (mid_idx == size - 1 || nums[mid_idx+1] > target)
                    {
                        range[1] = mid_idx;
                        break;
                    }
                    else
                        left_idx = mid_idx + 1;
                }
                else if (nums[mid_idx] < target)
                    left_idx = mid_idx + 1;
                else
                    right_idx = mid_idx - 1;
            }
        }

        if (range[1] == -1)
            range[1] = range[0];

        return range;        
    }
};
           

Runtime: 12 ms