Dada una array, encuentre el elemento menos frecuente en ella. Si hay varios elementos que aparecen la menor cantidad de veces, imprima cualquiera de ellos.
Ejemplos:
Input : arr[] = {1, 3, 2, 1, 2, 2, 3, 1}
Output : 3
3 appears minimum number of times in given
array.
Input : arr[] = {10, 20, 30}
Output : 10 or 20 or 30
Una solución simple es ejecutar dos bucles. El bucle exterior recoge todos los elementos uno por uno. El bucle interno encuentra la frecuencia del elemento elegido y la compara con el mínimo hasta el momento. La complejidad temporal de esta solución es O(n 2 )
Una mejor solución es clasificar. Primero ordenamos la array, luego recorremos linealmente la array.
C++
// CPP program to find the least frequent element
// in an array.
#include <bits/stdc++.h>
using namespace std;
int leastFrequent(int arr[], int n)
{
// Sort the array
sort(arr, arr + n);
// find the min frequency using linear traversal
int min_count = n+1, res = -1, curr_count = 1;
for (int i = 1; i < n; i++) {
if (arr[i] == arr[i - 1])
curr_count++;
else {
if (curr_count < min_count) {
min_count = curr_count;
res = arr[i - 1];
}
curr_count = 1;
}
}
// If last element is least frequent
if (curr_count < min_count)
{
min_count = curr_count;
res = arr[n - 1];
}
return res;
}
// driver program
int main()
{
int arr[] = {1, 3, 2, 1, 2, 2, 3, 1};
int n = sizeof(arr) / sizeof(arr[0]);
cout << leastFrequent(arr, n);
return 0;
}
Java
// Java program to find the least frequent element
// in an array.
import java.io.*;
import java.util.*;
class GFG {
static int leastFrequent(int arr[], int n)
{
// Sort the array
Arrays.sort(arr);
// find the min frequency using
// linear traversal
int min_count = n+1, res = -1;
int curr_count = 1;
for (int i = 1; i < n; i++) {
if (arr[i] == arr[i - 1])
curr_count++;
else {
if (curr_count < min_count) {
min_count = curr_count;
res = arr[i - 1];
}
curr_count = 1;
}
}
// If last element is least frequent
if (curr_count < min_count)
{
min_count = curr_count;
res = arr[n - 1];
}
return res;
}
// driver program
public static void main(String args[])
{
int arr[] = {1, 3, 2, 1, 2, 2, 3, 1};
int n = arr.length;
System.out.print(leastFrequent(arr, n));
}
}
/*This code is contributed by Nikita Tiwari.*/
Python3
# Python 3 program to find the least # frequent element in an array. def leastFrequent(arr, n) : # Sort the array arr.sort() # find the min frequency using # linear traversal min_count = n + 1 res = -1 curr_count = 1 for i in range(1, n) : if (arr[i] == arr[i - 1]) : curr_count = curr_count + 1 else : if (curr_count < min_count) : min_count = curr_count res = arr[i - 1] curr_count = 1 # If last element is least frequent if (curr_count < min_count) : min_count = curr_count res = arr[n - 1] return res # Driver program arr = [1, 3, 2, 1, 2, 2, 3, 1] n = len(arr) print(leastFrequent(arr, n)) # This code is contributed # by Nikita Tiwari.
C#
// C# program to find the least
// frequent element in an array.
using System;
class GFG {
static int leastFrequent(int[] arr, int n)
{
// Sort the array
Array.Sort(arr);
// find the min frequency
// using linear traversal
int min_count = n + 1, res = -1;
int curr_count = 1;
for (int i = 1; i < n; i++)
{
if (arr[i] == arr[i - 1])
curr_count++;
else
{
if (curr_count < min_count)
{
min_count = curr_count;
res = arr[i - 1];
}
curr_count = 1;
}
}
// If last element is least frequent
if (curr_count < min_count)
{
min_count = curr_count;
res = arr[n - 1];
}
return res;
}
// Driver code
static public void Main ()
{
int[] arr = {1, 3, 2, 1, 2, 2, 3, 1};
int n = arr.Length;
// Function calling
Console.Write(leastFrequent(arr, n));
}
}
// This code is contributed by Shrikant13
PHP
<?php
// PHP program to find the
// least frequent element
// in an array.
function leastFrequent($arr, $n)
{
// Sort the array
sort($arr);
sort($arr , $n);
// find the min frequency
// using linear traversal
$min_count = $n + 1;
$res = -1;
$curr_count = 1;
for($i = 1; $i < $n; $i++)
{
if ($arr[$i] == $arr[$i - 1])
$curr_count++;
else
{
if ($curr_count < $min_count)
{
$min_count = $curr_count;
$res = $arr[$i - 1];
}
$curr_count = 1;
}
}
// If last element is
// least frequent
if ($curr_count < $min_count)
{
$min_count = $curr_count;
$res = $arr[$n - 1];
}
return $res;
}
// Driver Code
{
$arr = array(1, 3, 2, 1, 2, 2, 3, 1);
$n = sizeof($arr) / sizeof($arr[0]);
echo leastFrequent($arr, $n);
return 0;
}
// This code is contributed by nitin mittal
?>
Javascript
<script>
// JavaScript program to find the least frequent element
// in an array.
function leastFrequent(arr, n)
{
// Sort the array
arr.sort();
// find the min frequency using
// linear traversal
let min_count = n+1, res = -1;
let curr_count = 1;
for (let i = 1; i < n; i++) {
if (arr[i] == arr[i - 1])
curr_count++;
else {
if (curr_count < min_count) {
min_count = curr_count;
res = arr[i - 1];
}
curr_count = 1;
}
}
// If last element is least frequent
if (curr_count < min_count)
{
min_count = curr_count;
res = arr[n - 1];
}
return res;
}
// Driver code
let arr = [1, 3, 2, 1, 2, 2, 3, 1];
let n = arr.length;
document.write(leastFrequent(arr, n));
</script>
Producción:
3
Complejidad de tiempo: O(n Log n)
Espacio auxiliar: O(1)
Una solución eficiente es usar hashing. Creamos una tabla hash y almacenamos elementos y su frecuencia cuenta como pares de valores clave. Finalmente recorremos la tabla hash e imprimimos la clave con el valor mínimo.
C++
// CPP program to find the least frequent element
// in an array.
#include <bits/stdc++.h>
using namespace std;
int leastFrequent(int arr[], int n)
{
// Insert all elements in hash.
unordered_map<int, int> hash;
for (int i = 0; i < n; i++)
hash[arr[i]]++;
// find the min frequency
int min_count = n+1, res = -1;
for (auto i : hash) {
if (min_count >= i.second) {
res = i.first;
min_count = i.second;
}
}
return res;
}
// driver program
int main()
{
int arr[] = {1, 3, 2, 1, 2, 2, 3, 1};
int n = sizeof(arr) / sizeof(arr[0]);
cout << leastFrequent(arr, n);
return 0;
}
Java
//Java program to find the least frequent element
//in an array
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
class GFG {
static int leastFrequent(int arr[],int n)
{
// Insert all elements in hash.
Map<Integer,Integer> count =
new HashMap<Integer,Integer>();
for(int i = 0; i < n; i++)
{
int key = arr[i];
if(count.containsKey(key))
{
int freq = count.get(key);
freq++;
count.put(key,freq);
}
else
count.put(key,1);
}
// find min frequency.
int min_count = n+1, res = -1;
for(Entry<Integer,Integer> val : count.entrySet())
{
if (min_count >= val.getValue())
{
res = val.getKey();
min_count = val.getValue();
}
}
return res;
}
// driver program
public static void main (String[] args) {
int arr[] = {1, 3, 2, 1, 2, 2, 3, 1};
int n = arr.length;
System.out.println(leastFrequent(arr,n));
}
}
// This code is contributed by Akash Singh.
Python3
# Python3 program to find the most # frequent element in an array. import math as mt def leastFrequent(arr, n): # Insert all elements in Hash. Hash = dict() for i in range(n): if arr[i] in Hash.keys(): Hash[arr[i]] += 1 else: Hash[arr[i]] = 1 # find the max frequency min_count = n + 1 res = -1 for i in Hash: if (min_count >= Hash[i]): res = i min_count = Hash[i] return res # Driver Code arr = [1, 3, 2, 1, 2, 2, 3, 1] n = len(arr) print(leastFrequent(arr, n)) # This code is contributed by # mohit kumar 29
C#
// C# program to find the
// least frequent element
// in an array.
using System;
using System.Collections.Generic;
class GFG
{
static int leastFrequent(int []arr,
int n)
{
// Insert all elements in hash.
Dictionary<int, int> count =
new Dictionary<int,
int>();
for (int i = 0; i < n; i++)
{
int key = arr[i];
if(count.ContainsKey(key))
{
int freq = count[key];
freq++;
count[key] = freq;
}
else
count.Add(key, 1);
}
// find the min frequency
int min_count = n + 1, res = -1;
foreach (KeyValuePair<int,
int> pair in count)
{
if (min_count >= pair.Value)
{
res = pair.Key;
min_count = pair.Value;
}
}
return res;
}
// Driver Code
static void Main()
{
int []arr = new int[]{1, 3, 2, 1,
2, 2, 3, 1};
int n = arr.Length;
Console.Write(leastFrequent(arr, n));
}
}
// This code is contributed by
// Manish Shaw(manishshaw1)
Javascript
<script>
// JavaScript program to find the least frequent element
// in an array.
function leastFrequent(arr, n)
{
// Insert all elements in hash.
var hash = new Map();
for (var i = 0; i < n; i++)
{
if(hash.has(arr[i]))
hash.set(arr[i], hash.get(arr[i])+1)
else
hash.set(arr[i], 1);
}
// find the min frequency
var min_count = n+1, res = -1;
hash.forEach((value, key) => {
if (min_count >= value) {
res = key;
min_count = value;
}
});
return res;
}
// driver program
var arr = [1, 3, 2, 1, 2, 2, 3, 1];
var n = arr.length;
document.write( leastFrequent(arr, n));
</script>
Producción:
3
Tiempo Complejidad : O(n)
Espacio Auxiliar : O(n)