C++ Toolbox

Vector

1. Init 2D vectors: https://stackoverflow.com/questions/17663186/initializing-a-two-dimensional-stdvector

    std::vector<std::vector<int> > v (A_NUMBER, std::vector <int> (OTHER_NUMBER, DEFAULT_VALUE))

2. Find an element in an array

   Simple version:

    vector<int> vc = {2,10};
    if(find(vc.begin(), vc.end(), 10) != vc.end())
        cout << "Found 10!";

   Generic version:

    template < typename T>
   std::pair<bool, int > findInVector(const std::vector<T>  & vecOfElements, const T  & element)
   {
    std::pair<bool, int > result;
   
    // Find given element in vector
    auto it = std::find(vecOfElements.begin(), vecOfElements.end(), element);
   
    if (it != vecOfElements.end())
    {
        result.second = distance(vecOfElements.begin(), it);
        result.first = true;
    }
    else
    {
        result.first = false;
        result.second = -1;
    }
   
    return result;

Sort

1. Sort vector of vector: https://stackoverflow.com/questions/14419520/sort-vector-of-vectors

    std::sort(vec.begin(), vec.end(),
              [](const std::vector<int>& a, const std::vector<int>& b) {
      return a[2] < b[2];
    });

2. Sum of vector elements: https://stackoverflow.com/questions/3221812/how-to-sum-up-elements-of-a-c-vector

    sum_of_elems = std::accumulate(vector.begin(), vector.end(), 0);

String

1. Substring http://www.cplusplus.com/reference/string/string/substr/

2. Replace http://www.cplusplus.com/reference/string/string/replace/

3. back http://www.cplusplus.com/reference/string/string/back/

4. pop_back

5. convert string to int - stoi http://www.cplusplus.com/reference/string/stoi/

6. erase http://www.cplusplus.com/reference/string/string/erase/

7. insert http://www.cplusplus.com/reference/string/string/insert/

8. Tokenize https://www.geeksforgeeks.org/tokenizing-a-string-cpp/

    // Tokenize w.r.t. space ' '
    string s = "I love leetcode, leetcode loves me."
    vector<string> tokens;
    stringstream ss(s); 
    string tok; 
   
    while(getline(ss, tok, ' ')) { 
        if(tok == " " || tok == "") continue;
        tokens.push_back(tok); 
    }

   Another way: https://stackoverflow.com/questions/236129/how-do-i-iterate-over-the-words-of-a-string

9. convert string element to int (or back)

   https://stackoverflow.com/questions/5290089/how-to-convert-a-number-to-string-and-vice-versa-in-c

10. Convert int to char

    • In C++17, use std::to_chars as:

    std::array<char, 10> str;
    std::to_chars(str.data(), str.data() + str.size(), 42);

    • In C++11, use std::to_string as:

    std::string s = std::to_string(number);
    char const *pchar = s.c_str();  //use char const* as target type

Priority_queue

1. Create a min-heap:

    std::priority_queue<int, std::vector<int>, std::greater<int> > my_min_heap;

2. Store my own data structure:https://stackoverflow.com/questions/16111337/declaring-a-priority-queue-in-c-with-a-custom-comparator/48587737

    class rate_pair
    {
    public:
        int index;
        int rate;
   
        rate_pair(int id, int r) {
            index = id;
            rate = r;
        }
    };
   
    class Compare
    {
    public:
        bool operator() (rate_pair rate_pair_1, rate_pair rate_pair_2)
        {
            return rate_pair_1.rate > rate_pair_2.rate;
        }
    };
   
    class Solution {
    public:
        int candy(vector<int>& ratings) {
            // Corner case
            if(ratings.size() < 2) return ratings.size();
   
            // Use a pq to hold ratings 
            priority_queue<rate_pair, std::vector<rate_pair>, Compare> pq;
            for(int i=0; i<ratings.size(); i++) {
                rate_pair r(i, ratings[i]);
                pq.push(r);
            }
   
            while(!pq.empty()) {
                cout << pq.top().index << " " << pq.top().rate << endl;
                pq.pop();
            }
   
            vector<int> candy(ratings.size(), 1);
   
            return accumulate(candy.begin(), candy.end(), 0);
        }
    };

Set

1. Custom comparator

   https://stackoverflow.com/a/46128321/1128197