String

1. Erase all the occurrences of char (e.g., 'a') in a string:

#include <algorithm>
str.erase(std::remove(str.begin(), str.end(), 'a'), str.end());

2. Find all the substring p in s:

for(size_t i = 0; (i = s.find(p,i)) != string::npos; ++i) {
    pos.emplace_back(i);
}

3. Split the string based on pattern

vector<string> split(const string &str, const string& pattern) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(pattern, start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));
        start = end + pattern.size();
    }

    tokens.push_back(str.substr(start));

    return tokens;
}

4. Find repetitive substring

E.g., s="abcabcabc" is reprtitive based on "abc".

string repetitiveSubstring(const string& s) {
    int pos = (s+s).find(s,1);
    if ( pos < s.size() ) { // has substring repetition in s
        return s.substr(0, pos);
    }
    return "";
}