Date: 16 Oct 2022

Frequency Map

Frequency of each character in a String

Approach

Traverse each of the character in the String
Check whether the current character is present in the Map
If present the update the frequency else insert in the Map;

Example:

    // C++
    string s = "abccccdd";
    
    for (char c : s)
        map[c]++;

    // Java
    String s = "abccccdd";
    
    for (char c : s.toCharArray())
        map.merge(c, 1, Integer::sum);        

C++ naive

    #include <iostream>
    #include <unordered_map>
    using namespace std;

    int main() {
        string s = "abccccdd";
        unordered_map<char, int> map;

        for (int i = 0; i < s.length(); i++){
            if (map.find(s[i]) == map.end())
                map.insert(make_pair(s[i], 1);
            else
                map[s[i]]++;
        }

        // print
        for (auto& it : map) {
            cout << it.first << ' ' << it.second << '\n';
        }
        return 0;
    }

C++ elegant ;-)

    #include <iostream>
    #include <unordered_map>
    using namespace std;

    int main() {
        string s = "abccccdd";
        unordered_map<char, int> map;

        for (char c : s)
            map[c]++;

        // print
        for (auto& it : map) {
            cout << it.first << ' ' << it.second << '\n';
        }
        return 0;
    }

<= Java7 naive

    import java.util.Map;
    public class Main {
        public static void main(String[] args) {
            String s = "abccccdd";
            Map<Character, Integer> map = new HashMap<>();
            for (int i = 0; i < s.length(); i++) {
                if (map.containsKey(s.charAt(i))) {
                    map.put(s.charAt(i), map.get(s.charAt(i)) + 1);
                } else {
                    map.put(s.charAt(i), 1);
                }
            }

            // print
            for (Map.Entry e : map.entrySet()) {
                System.out.println(e.getKey() + " " + e.getValue());
            }
        }
    }

Java 8+ elegant ;-)

    import java.util.Map;
    import java.util.HashMap;
    public class Main {
        public static void main(String[] args) {
            String s = "abccccdd";
            Map<Character, Integer> map = new HashMap<>();

            for (char c : s.toCharArray())
                map.merge(c, 1, Integer::sum);

            // print
            for (Map.Entry e : map.entrySet())
                System.out.println(e.getKey() + " " + e.getValue());
        }
    }