Finding common characters in two strings

Question

I am coding for the problem in which we got to count the number of common characters in two strings. Main part of the count goes like this

for(i=0; i < st         


        

Answer 1

First, your code does not run in O(n^2), it runs in O(nm), where n and m are the length of each string.

You can do it in O(n+m), but not better, since you have to go through each string, at least once, to see if a character is in both.

An example in C++, assuming:

• ASCII characters
• All characters included (letters, numbers, special, spaces, etc...)
• Case sensitive

std::vector strIntersect(std::string const&s1, std::string const&s2){

    std::vector presents(256, false);  //Assuming ASCII
    std::vector intersection;

    for (auto c : s1) {
        presents[c] = true;
    }
    for (auto c : s2) {
        if (presents[c]){
            intersection.push_back(c);
            presents[c] = false;
        }
    }
    return intersection;
}

int main() {
    std::vector result; 
    std::string s1 = "El perro de San Roque no tiene rabo, porque Ramon Rodriguez se lo ha cortado";
    std::string s2 = "Saint Roque's dog has no tail, because Ramon Rodriguez chopped it off";

    //Expected: "S a i n t   R o q u e s d g h l , b c m r z p"

    result = strIntersect(s1, s2);
    for (auto c : result) {
         std::cout << c << " ";
    }
    std::cout << std::endl;

    return 0;
}