经典二分左右模版方法logn复杂度

class Solution {
public:
    int getNumberOfK(vector<int>& nums , int k) {

        int left_index = getLeft(nums,k,0,nums.size());
        int right_index = getRight(nums,k,left_index,nums.size());

        return right_index - left_index + 1;

    }


    int getLeft(vector<int>& nums,int target, int left,int right)
    {

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


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