Given an array of integers, replace every element by its frequency in the array.
Examples:
Input : arr[] = { 1, 2, 5, 2, 2, 5 }
Output : 1 3 2 3 3 2
Input : arr[] = { 4 5 4 5 6 6 6 }
Output : 2 2 2 2 3 3 3
Approach:
- Take a hash map, which will store the frequency of all the elements in the array.
- Now, traverse once again.
- Now, replace all the elements by their frequency.
- Print the modified array.
Implementation:
C++
// C++ program to replace the elements// by their frequency in the array.#include "iostream"#include "unordered_map"using namespace std;void ReplaceElementsByFrequency(int arr[], int n){ // Hash map which will store the // frequency of the elements of the array. unordered_map<int, int> mp; for (int i = 0; i < n; ++i) { // Increment the frequency // of the element by 1. mp[arr[i]]++; } // Replace every element by its frequency for (int i = 0; i < n; ++i) { arr[i] = mp[arr[i]]; }}int main(){ int arr[] = { 1, 2, 5, 2, 2, 5 }; int n = sizeof(arr) / sizeof(arr[0]); ReplaceElementsByFrequency(arr, n); // Print the modified array. for (int i = 0; i < n; ++i) { cout << arr[i] << " "; } return 0;} |
Java
import java.util.HashMap;// Java program to replace the elements // by their frequency in the array.class GFG { static void ReplaceElementsByFrequency(int arr[], int n) { // Hash map which will store the // frequency of the elements of the array. HashMap<Integer, Integer> mp = new HashMap<Integer, Integer>(); for (int i = 0; i < n; ++i) { // Increment the frequency // of the element by 1. if (mp.get(arr[i]) == null) { mp.put(arr[i], 1); } else { mp.put(arr[i], (mp.get(arr[i]) + 1)); } //mp[arr[i]]++; } // Replace every element by its frequency for (int i = 0; i < n; ++i) { if (mp.get(arr[i]) != null) { arr[i] = mp.get(arr[i]); } //arr[i] = mp[arr[i]]; } } public static void main(String[] args) { int arr[] = {1, 2, 5, 2, 2, 5}; int n = arr.length; ReplaceElementsByFrequency(arr, n); // Print the modified array. for (int i = 0; i < n; ++i) { System.out.print(arr[i] + " "); } }}// This code contributed by 29AJayKumar |
Python3
# Python 3 program to replace the elements# by their frequency in the array.def ReplaceElementsByFrequency(arr, n): # Hash map which will store the # frequency of the elements of the array. mp = {i:0 for i in range(len(arr))} for i in range(n): # Increment the frequency of the # element by 1. mp[arr[i]] += 1 # Replace every element by its frequency for i in range(n): arr[i] = mp[arr[i]]# Driver Codeif __name__ == '__main__': arr = [1, 2, 5, 2, 2, 5] n = len(arr) ReplaceElementsByFrequency(arr, n); # Print the modified array. for i in range(n): print(arr[i], end = " ")# This code is contributed by# Sahil_shelangia |
C#
// C# program to replace the elements // by their frequency in the array.using System;using System.Collections.Generic; class GFG { static void ReplaceElementsByFrequency(int []arr, int n) { // Hash map which will store the // frequency of the elements of the array. Dictionary<int,int> mp = new Dictionary<int,int>(); for (int i = 0; i < n; ++i) { // Increment the frequency // of the element by 1. if (!mp.ContainsKey(arr[i])) { mp.Add(arr[i], 1); } else { var a = mp[arr[i]] + 1; mp.Remove(arr[i]); mp.Add(arr[i], a); } } // Replace every element by its frequency for (int i = 0; i < n; ++i) { if (mp[arr[i]] != 0) { arr[i] = mp[arr[i]]; } //arr[i] = mp[arr[i]]; } } // Driver code public static void Main(String[] args) { int []arr = {1, 2, 5, 2, 2, 5}; int n = arr.Length; ReplaceElementsByFrequency(arr, n); // Print the modified array. for (int i = 0; i < n; ++i) { Console.Write(arr[i] + " "); } }}// This code contributed by Rajput-Ji |
Javascript
<script>// JavaScript program to replace the elements // by their frequency in the array.function ReplaceElementsByFrequency(arr, n) { // Hash map which will store the // frequency of the elements of the array. let mp = new Map(); for(let i = 0; i < n; ++i) { // Increment the frequency // of the element by 1. if (mp.get(arr[i]) == null) { mp.set(arr[i], 1); } else { mp.set(arr[i], (mp.get(arr[i]) + 1)); } //mp[arr[i]]++; } // Replace every element by its frequency for(let i = 0; i < n; ++i) { if (mp.get(arr[i]) != null) { arr[i] = mp.get(arr[i]); } //arr[i] = mp[arr[i]]; }}// Driver Codelet arr = [ 1, 2, 5, 2, 2, 5 ];let n = arr.length;ReplaceElementsByFrequency(arr, n);// Print the modified array. for(let i = 0; i < n; ++i){ document.write(arr[i] + " ");}// This code is contributed by code_hunt</script> |
Output
1 3 2 3 3 2
Time Complexity: O(N)
Auxiliary Space: O(N) because extra space is being used for unordered_map mp
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