Find frequency of each character with positions in given Array of Strings

import java.util.*;
import java.util.Map.Entry;

class GFG {
  public static void printOccurrences(List<String> arr, int N) {
    Map<Character, List<Pair<Integer, Integer>>> mp = new HashMap<>();

    // Iterate over the List arr[]
    for (int i = 0; i < N; i++) 
    {
      
      // Traverse the string arr[i]
      for (int j = 0; j < arr.get(i).length(); j++)
      {
        
        // Push the pair of{i+1, j+1}
        // in mp[arr[i][j]]
        if (!mp.containsKey(arr.get(i).charAt(j))) {
          mp.put(arr.get(i).charAt(j), new ArrayList<>());
        }
        mp.get(arr.get(i).charAt(j)).add(new Pair<>(i + 1, j + 1));
      }
    }
    
    // Print the occurrences of every
    // character
    for (Entry<Character, List<Pair<Integer, Integer>>> it : mp.entrySet()) {
      System.out.print("Occurrences of: " + it.getKey() + " = ");
      for (int j = 0; j < it.getValue().size(); j++) {
        System.out.print("[" + it.getValue().get(j).getKey() + " " + it.getValue().get(j).getValue() + "] ");
      }
      System.out.println();
    }
  }

  // Driver Code
  public static void main(String[] args) 
  {
    
    // Input
    List<String> arr = Arrays.asList("geeksforgeeks", "gfg");
    int N = arr.size();
    
    // Function call
    printOccurrences(arr, N);
  }
}

// custom pair class
class Pair<T, U> {
    private T key;
    private U value;

    public Pair(T key, U value) {
        this.key = key;
        this.value = value;
    }

    public T getKey() {
        return key;
    }

    public U getValue() {
        return value;
    }
}

// This code is contributed by aadityapburujwale