Most Common Word

Given a paragraph and a list of banned words, return the most frequent word that is not in the list of banned words.  It is guaranteed there is at least one word that isn't banned, and that the answer is unique.

Words in the list of banned words are given in lowercase, and free of punctuation.  Words in the paragraph are not case-sensitive.  The answer is in lowercase.

Example

Input: 
paragraph = "Bob hit a ball, the hit BALL flew far after it was hit."
banned = ["hit"]
Output: "ball"

Approach:

C++

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

string mostCommonWord(string paragraph, vector<string> &banned)
{
    int n = paragraph.size();
    map<string, int> mp;
    int i = 0;
    set<string> st;
    for (int i = 0; i < banned.size(); i++)
    {
        st.insert(banned[i]);
    }
    while (i < n)
    {
        string str = "";
        while (i < n && !isalpha(paragraph[i]))
        {
            i++;
        }
        while (i < n && paragraph[i] != ' ' && isalpha(paragraph[i]))
        {
            if (paragraph[i] >= 'A' && paragraph[i] <= 'Z')
            {
                str += paragraph[i] + 32;
            }
            else
            {
                str = str + paragraph[i];
            }
            i++;
        }
        if (st.find(str) != st.end())
            continue;
        else
        {
            if (str.size() > 0)
                mp[str]++;
        }
    }
    int max1 = INT_MIN;
    string res = "";
    for (auto it = mp.begin(); it != mp.end(); it++)
    {
        if (it->second > max1)
        {
            max1 = it->second;
            res = it->first;
        }
    }
    return res;
}

int main()
{
    string paragraph = "Bob hit a ball, the hit BALL flew far after it was hit.";
    vector<string> banned = {"hit"};
    cout << mostCommonWord(paragraph, banned);

    return 0;
}