# Cyberlink CV
###### tags: `Interviews`

## Interview questions
1. 全連接跟卷積差別在哪?為什麼CV用卷積居多？ 優勢是什麼？
捕捉空間特徵？參數可複用減少運算 另外也可捕捉重複特徵？

2. 激勵函數引入非線性的目的是什麼？如果只有線性會怎樣？
實際問題很多情況都非線性，不是能靠線性函數解決 *可以補充sigmoid, tanh, relu, softmax...各自帶來的優點
[without activation function](https://www.analyticsvidhya.com/blog/2020/01/fundamentals-deep-learning-activation-functions-when-to-use-them/)

3. Self supervised learning, GAN, Model compression, Model compression, Knowledge distillation, Image classification, object detection, Super resolution這幾個去分類 你會分幾類？怎麼分？

4. 你處理過最難的bug是什麼?

6. 碩班期間，老闆給你的彈性如何?方向跟方法多少是自己決定的?

7. 有沒有老闆覺得目標或方法可行，但你覺得不可行的時候，怎麼處理和最後結果如何?

8. 做過的專案中的這些模型你是直接使用，還是有做什麼調整嗎?

9. 請簡介一個深度學習模型專案流程，並說明如何評估表現?如果表現不夠好，最可能出問題的地方在哪?應該如何調整?

10. CV相關的議題可以舉出哪些?如果有機會錄取，最想做哪一個?

## Coding test
測驗環境(網站)是**Coderbyte**
### BinaryReversal
1. 給一個string的二進位值要從大的位數開始補滿0到8*N bits 補滿之後再反轉 反轉完再換回10進位
* Key:
a. reverse string : swap記得call by reference, size要size-i-1因為string最後一個位置是'\0'
b. binary有可能超過int大小 所以用long long
c. stoi跟to_string要熟悉

* Test cases:
"47" ->101111-> 00101111->11110100->244
"213" -> 171
"4567" -> 60296
"12" -> 1100 -> 00001100 -> 00110000 -> 48

### My solution

#include <iostream>
#include <string>
#include<math.h>
using namespace std;

void swap(string &s, int a, int b)
{
	s[a] = s[a] ^ s[b];
	s[b] = s[a] ^ s[b];
	s[a] = s[a] ^ s[b];
}

string BinaryReversal(string str) {

	cout << str;
	cout << endl;
    // string to integer 
	int num = stoi(str);

	long long binary = 0, remainder, product = 1;
	while (num != 0)
	{
		remainder = num % 2;
		binary += remainder * product;
		num = num / 2;
		product *= 10;
	}

	string str1 = to_string(binary);
    
    //complement to 8*N bytes
	while (str1.size()%8 != 0)
	{
		str1 = '0' + str1;
	}

    //reverse string
	for (int i = 0; i < str1.size() / 2; i++)
	{
		swap(str1, i, str1.size() - i - 1);
	}

    //bin to decimal 
	int ans = 0;
	int j = 0;
	for (int i = str1.size() - 1; i >= 0; i--)
	{
		if (str1[i] == '1')
		{
			ans += pow(2, j);
		}
		j++;
	}

	return to_string(ans);

}
int main()
{
	string str = "4567";
	string ans_str = BinaryReversal(str);
	cout << ans_str;
	return 0;
}

### ArrayMatching
2. 一個string array裡面有兩個陣列 要把兩個陣列對應的元素相加(第一個加第一個 第二個加第二個...) 如果陣列不等長 剩下的元素就不用加 然後每個元素相加完的結果用字串表示 元素間要以'-'區隔
* Key:
a. atoi的input format是const char*且只能轉超過single digit的數，char要強轉成const char*，single digit直接char - '0'
b. stoi的input format是const string
* Test case:
["[1, 2, 5, 6]", "[5, 2, 8, 11]"]->6-4-13-17
["[1, 2, 5, 6, 7, 9]", "[5, 2, 8, 11]"]->6-4-13-17-7-9
["[1, 2, 5, 6]", "[5, 2, 8, 11, 7, 9]"]->6-4-13-17-7-9

### My solution

#include "pch.h"
#include <iostream>
#include <string>
#include <string.h>
#include<vector>
using namespace std;

vector<int> strtoArr(string Arr)
{
	int tmp = 0;
	vector<int> arr;
	for (int i = 0; i < Arr.size(); i++)
	{

		if (Arr[i] != ' '&& Arr[i] != '[')
		{
			if (Arr[i] != ','&& Arr[i] != ']')
			{
				tmp = tmp * 10 + (Arr[i] - 48);
			}
			else
			{
				arr.push_back(tmp);
				tmp = 0;
			}
		}

	}
	return arr;
}

string ArrayMatching(string strArr[], int arrLength) { 

	vector<int> nums;
	vector<int> nums2;
        nums = strtoArr(strArr[0]);
        nums2 = strtoArr(strArr[1]);

	string ans;
	if (nums.size() > nums2.size())
	{
		for (int i = 0; i < nums2.size(); i++)
		{
			nums[i] += nums2[i];
		}
		for (int j = 0; j < nums.size(); j++)
		{
			ans += to_string(nums[j]);
			if (j != nums.size() - 1)
			{
				ans += '-';
			}
		}
		//cout<<ans;
		return ans;
	}

	else {
		for (int i = 0; i < nums.size(); i++)
		{
			nums2[i] += nums[i];
		}
		for (int j = 0; j < nums2.size(); j++)
		{
			ans += to_string(nums2[j]);
			if (j != nums2.size() - 1)
			{
				ans += '-';
			}
		}
		//cout<<ans;
		return ans;
	}


}

int main(void) {

	// keep this function call here
	string A[] = {"[1, 2, 5, 6]", "[5, 2, 8, 11, 7, 9]"};
	int arrLength = sizeof(A) / sizeof(*A);
	cout << ArrayMatching(A, arrLength);
	return 0;

}

3. LRU Cache
>Have the function LRUCache(strArr) take the array of characters stored in strArr, which will contain characters ranging from A to Z in some arbitrary order, and determine what elements still remain in a virtual cache that can hold up to 5 elements with an LRU cache algorithm implemented. For example: if strArr is ["A", "B", "C", "D", "A", "E", "D", "Z"], then the following steps are taken:
>
>(1) A does not exist in the cache, so access it and store it in the cache.
(2) B does not exist in the cache, so access it and store it in the cache as well. So far the cache contains: ["A", "B"].
(3) Same goes for C, so the cache is now: ["A", "B", "C"].
(4) Same goes for D, so the cache is now: ["A", "B", "C", "D"].
(5) Now A is accessed again, but it exists in the cache already so it is brought to the front: ["B", "C", "D", "A"].
(6) E does not exist in the cache, so access it and store it in the cache: ["B", "C", "D", "A", "E"].
(7) D is accessed again so it is brought to the front: ["B", "C", "A", "E", "D"].
(8) Z does not exist in the cache so add it to the front and remove the least recently used element: ["C", "A", "E", "D", "Z"].

>Now the caching steps have been completed and your program should return the order of the cache with the elements joined into a string, separated by a hyphen. Therefore, for the example above your program should return C-A-E-D-Z.

### LRUCache
>leetcode : https://leetcode.com/problems/lru-cache/
* key
a. 為了找有沒有出現過->set->但set要刪除特定元素還是要迭代
b. 為了方便pop掉最後一個出現的元素->queue->但queue在迭代每一個元素確認是否出現過要一直pop跟push
c. 最後還是用vector
d. ~~這題雖然medium 但感覺沒前兩題難~~
* Test case
Examples
Input: {"A", "B", "A", "C", "A", "B"}
Output: C-A-B
Input: {"A", "B", "C", "D", "E", "D", "Q", "Z", "C"}
Output: E-D-Q-Z-C

### My solution

#include "pch.h"
#include<string>
#include<vector>
#include <iostream>
using namespace std;

string LRUCache(string strArr[], int arrLength)
{
	vector<string> cache;
	string tmp, ansStr;

	cache.push_back(strArr[0]);
	//loop the array and save to cache
	for (int i = 1; i < arrLength; i++)
	{
	//check if cache have 5 objects 
		if (cache.size() < 5)
		{
		//check if it exits. if yes, find where is it and swap with last one
			int cacheSize = cache.size();
			for (int j = 0; j < cacheSize;j++)
			{
				if (cache[j] == strArr[i])
				{
					cache.erase(cache.begin()+j);
					cache.push_back(strArr[i]);
					break;
				}
				else
				{
					// if not, push it back
					if (j == cacheSize-1)
					{
						cache.push_back(strArr[i]);
					}
				}
			}
			
		}
	//if yes, pop the first one (least use one) and push to the last one
		else
		{
			cache.erase(cache.begin());
			cache.push_back(strArr[i]);
		}
	}

	for (int i = 0; i < cache.size(); i++)
	{
		ansStr += cache[i];
		if (i != cache.size() - 1)
		{
			ansStr += '-';
		}
	}
	
	
	return ansStr;
}

int main()
{
	string A[] = { "A", "B", "C", "D", "E", "D", "Q", "Z", "C" };
	int arrLength = sizeof(A) / sizeof(*A);
	string ans = LRUCache(A, arrLength);
	//cout << endl;
	//cout << ans;
	return 0;
}

## Reference
[string to array](https://www.geeksforgeeks.org/convert-a-string-to-integer-array-in-c-c/)
[atoi & stoi](https://www.796t.com/content/1548701299.html)
[char to const char to string...](https://blog.csdn.net/rongrongyaofeiqi/article/details/52442169)
[queue iteration](https://stackoverflow.com/questions/1259099/stdqueue-iteration)