answer1.cpp

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

/**
 * If the 2nd array is a subset of 1st array, return true.
 * Time complexity: O(N+M)
 * M : A length
 * N : B length
 * 
 * Space complexity: O(26)
 * @param chars .
 */
bool isSubset(vector<char>& A, vector<char>& B){
    vector<int> letters(26);
    for (char c : A){
        // c - 'A' will generate the code as below.
        // A => 0, B => 1, C = 2
        letters[c - 'A']++;
    }

    for (char c : B){
        if(letters[c - 'A'] == 0){
            return false;
        }
    }
    return true;
}

int main()
{
    vector<char> a {'A','C','D','D','A'};
    vector<char> b {'A','D'};
    bool result = isSubset(a,b); // true
}