Longest Common Substring [NCTU Floor 18]

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>

using namespace std;

void solving(string x, string y, int lx, int ly){
    vector <string> res;
    vector <vector <int>> mark(lx, vector <int>(ly));
    int max = 0;
    for(int i = 0; i < lx; i++){
        for(int j = 0; j < ly; j++){
            if(x[i] != y[j]){
                mark[i][j] = 0;
                continue;
            }
            if(i == 0 || j == 0){
                mark[i][j] = 1;
            }else{
                mark[i][j] = mark[i - 1][j - 1] + 1;
            }
            if(mark[i][j] > max){
                max = mark[i][j];
                res.clear();
                res.push_back(x.substr(i + 1 - max, (i + 1) - (i + 1 - max)));
            }else if(mark[i][j] == max){
                res.push_back(x.substr(i + 1 - max, (i + 1) - (i + 1 - max)));
            }
        }
    }
    sort(res.begin(), res.end());
    cout << res[0] << endl;
}

string evolve(string temp){
    string a = temp;
    a.erase(remove_if(a.begin(), a.end(), [](char c){
        return c == ',' || c == '.' || c == '!' || c == '?';
        }), a.end());
    transform(a.begin(), a.end(), a.begin(), ::toupper);
    return a;
}

int main(){
    string x, y;
    cin >> x >> y;

    string X = evolve(x);
    string Y = evolve(y);

    int m = x.length();
    int n = y.length();

    solving(X, Y, m, n);
    return 0;
}