CPP Cheat Sheet

Table of Contents

Data Structures

String

• Return a substring using substring(start_position, length)

    // (quoting Alfred N. Whitehead)
    std::string str="We think in generalities, but we live in details.";
    std::string str2 = str.substr(3,5); // "think"

• Find a substring using find(sub_string)

    std::size_t pos = str.find("live");   

Set

• Inititalize a set from a vector

    vector<string> words{"one", "two"};
    set<string> words_set(words.begin(), words.end());

Map

• Using unordered_map

	unordered_map<string, string> umap = {
		{"RED", "#FF0000"},
		{"GREEN", "#00FF00"}
	};
	
	// Output the key and value of map
	for (auto color: umap) {
		cout<<color.first<<" "<<color.second<<endl;
	}

• Using iterator

	map<int, string> my_map;
    my_map[1] = "first";
    my_map[2] = "second";
    
    for (map<int, string>::iterator it=my_map.begin(); it!= my_map.end(); it++) {
        cout<<(*it).first<<" "<<(*it).second<<endl;
    }

Priority Queue

• Initialize a standard priority queue

    vector<int> input{1, 8, 5, 4, 6, 7};

    // Create a max heap
    priority_queue<int> maxQueue(input.begin(), input.end());
    print_queue(maxQueue);

    // Create a min heap
    priority_queue<int, vector<int>, greater<int>> minQueue(input.begin(), input.end());
    print_queue(minQueue);

• Create customer sort function

struct CustomComparator{
    bool operator()(int a, int b) {
        return a>b;
    }
};

int main() {
    vector<int> input{1, 8, 5, 4, 6, 7};
    // Create a custom sort heap
    priority_queue<int, vector<int>, CustomComparator> customQueue(input.begin(), input.end());
    print_queue(customQueue);
}

• Print a priority queue

    template<typename T>
    void print_queue(T &q) {
        while (!q.empty()) {
            cout << q.top() << " ";
            q.pop();
        }
        cout<<endl;
    }

Algorithms

Sort

• Sort a vector

    vector<int> nums{1,3,4,5,6};
    
    // Sort ascending
    sort(nums.begin(), nums.end());
    for (int i=0; i<nums.size(); i++) {
        cout<<nums[i]<<" ";
    }
    cout<<endl;
    // Sort decending
    sort(nums.begin(), nums.end(), greater<int>());
    for (int i=0; i<nums.size(); i++) {
        cout<<nums[i]<<" ";
    }

• Custom sort

Articles

1. Big-O cheat sheet.
2. TopCoder tutorial.