String Matching in an Array

Given an array of string words. Return all strings in words which is a substring of another word in any order. 
String words[i] is substring of words[j], if can be obtained removing some characters to left and/or right side of words[j].

Example 1:

Input: words = ["mass","as","hero","superhero"]
Output: ["hero","as"]

Approach

Java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;

public class StringMatchingInArray {
    public static void main(String[] args) {
        String[] words = { "mass", "as", "hero", "superhero" };
        List<String> match = stringMatching(words);
        System.out.println(Arrays.asList(match));
    }

    static List<String> stringMatching(String[] words) {
        List<String> res = new ArrayList<String>();
        HashSet<String> st = new HashSet<String>();
        int n = words.length;
        for (int i = 0; i < n; i++) {
            String str = words[i];
            for (int j = 0; j < n; j++) {
                String s = words[j];
                if (i != j) {
                    if (s.length() >= str.length()) {
                        for (int k = 0; k <= s.length() - str.length(); k++) {
                            int flag = 0;
                            for (int l = 0; l < str.length(); l++) {
                                if (str.charAt(l) != s.charAt(l + k)) {
                                    flag = 1;
                                    break;
                                }
                            }
                            if (flag == 0) {
                                st.add(str);
                                break;
                            }
                        }
                    }
                }
            }
        }

        Iterator<String> it = st.iterator();
        while (it.hasNext())
            res.add(it.next());
        return res;
    }
}

C++

#include <bits/stdc++.h>
using namespace std;


vector<string> stringMatching(vector<string> &words)
{
    vector<string> res;
    unordered_set<string> st;
    int n = words.size();
    for (int i = 0; i < n; i++)
    {
        string str = words[i];
        for (int j = 0; j < n; j++)
        {
            string s = words[j];
            if (i != j)
            {
                if (s.size() >= str.size())
                {
                    for (int k = 0; k <= s.size() - str.size(); k++)
                    {
                        int flag = 0;
                        for (int l = 0; l < str.size(); l++)
                        {
                            if (str[l] != s[l + k])
                            {
                                flag = 1;
                                break;
                            }
                        }
                        if (flag == 0)
                        {
                            st.insert(str);
                            break;
                        }
                    }
                }
            }
        }
    }
    for (auto it = st.begin(); it != st.end(); it++)
        res.push_back(*it);
    return res;
}
int main()
{
    vector<string> words = {"mass", "as", "hero", "superhero"};
    vector<string> match = stringMatching(words);
    for (int i = 0; i < match.size(); i++)
        cout << match[i] << " ";
    return 0;
}