Check if all subarrays contains at least one unique element
Last Updated :
15 Jul, 2025
Given an array arr[] consisting of N integers, the task is to check if all subarrays of the array have at least one unique element in it or not. If found to be true, then print "Yes". Otherwise, print "No".
Examples:
Input: arr[] = {1, 2, 1}
Output: Yes
Explanation:
For Subarrays of size 1: {1}, {2}, {1}, the condition will always be true.
For Subarrays of size 2: {1, 2}, {2, 1}, each subarray has at least one unique element.
For Subarrays of size 3 = {1, 2, 1}, in this subarray we have 2 as the only unique element.
Since each subarray has at least one unique element, print "Yes".
Input: arr[] = {1, 2, 3, 1, 2, 3}
Output: No
Explanation:
Subarrays of size 6: {1, 2, 3, 1, 2, 3} contains no unique element. Therefore, print "No".
Naive Approach: The simplest approach is to generate all subarrays and use HashMap for each subarray to store the frequency of each element of that subarray. If any subarray does not have at least one unique element, then print "No". Otherwise, print "Yes".
Below is the implementation of the above approach:
C++
// C++ program for above approach
#include<bits/stdc++.h>
using namespace std;
// Function to check if all subarrays
// of array have at least one unique element
string check(int arr[], int n)
{
// Stores frequency of subarray
// elements
map<int, int> hm;
// Generate all subarrays
for(int i = 0; i < n; i++)
{
// Insert first element in map
hm[arr[i]] = 1;
for(int j = i + 1; j < n; j++)
{
// Update frequency of current
// subarray in the HashMap
hm[arr[j]]++;
bool flag = false;
// Check if at least one element
// occurs once in current subarray
for(auto x : hm)
{
if (x.second == 1)
{
flag = true;
break;
}
}
// If any subarray doesn't
// have unique element
if (!flag)
return "No";
}
// Clear map for next subarray
hm.clear();
}
// Return Yes if all subarray
// having at least 1 unique element
return "Yes";
}
// Driver Code
int main()
{
// Given array arr[]
int arr[] = { 1, 2, 1 };
int N = sizeof(arr) / sizeof(arr[0]);
// Function Call
cout << check(arr, N);
}
// This code is contributed by bgangwar59
// Java program for above approach
import java.util.*;
import java.lang.*;
class GFG {
// Function to check if all subarrays
// of array have at least one unique element
static String check(int arr[], int n)
{
// Stores frequency of subarray
// elements
Map<Integer, Integer> hm
= new HashMap<>();
// Generate all subarrays
for (int i = 0; i < n; i++) {
// Insert first element in map
hm.put(arr[i], 1);
for (int j = i + 1; j < n; j++) {
// Update frequency of current
// subarray in the HashMap
hm.put(
arr[j],
hm.getOrDefault(arr[j], 0) + 1);
boolean flag = false;
// Check if at least one element
// occurs once in current subarray
for (Integer k : hm.values()) {
if (k == 1) {
flag = true;
break;
}
}
// If any subarray doesn't
// have unique element
if (!flag)
return "No";
}
// Clear map for next subarray
hm.clear();
}
// Return Yes if all subarray
// having at least 1 unique element
return "Yes";
}
// Driver Code
public static void main(String[] args)
{
// Given array arr[]
int[] arr = { 1, 2, 1 };
int N = arr.length;
// Function Call
System.out.println(check(arr, N));
}
}
# Python3 program for
# the above approach
from collections import defaultdict
# Function to check if
# all subarrays of array
# have at least one unique
# element
def check(arr, n):
# Stores frequency of
# subarray elements
hm = defaultdict (int)
# Generate all subarrays
for i in range(n):
# Insert first element
# in map
hm[arr[i]] += 1
for j in range(i + 1, n):
# Update frequency of
# current subarray in
# the HashMap
hm[arr[j]] += 1
flag = False
# Check if at least one
# element occurs once in
# current subarray
for k in hm.values():
if (k == 1):
flag = True
break
# If any subarray doesn't
# have unique element
if (not flag):
return "No"
# Clear map for next
# subarray
hm.clear()
# Return Yes if all
# subarray having at
# least 1 unique element
return "Yes"
# Driver Code
if __name__ == "__main__":
# Given array arr[]
arr = [1, 2, 1]
N = len(arr)
# Function Call
print(check(arr, N))
# This code is contributed by Chitranayal
// C# program for the
// above approach
using System;
using System.Collections.Generic;
class GFG{
// Function to check if all
// subarrays of array have at
// least one unique element
static String check(int []arr,
int n)
{
// Stores frequency of
// subarray elements
Dictionary<int,
int> hm =
new Dictionary<int,
int>();
// Generate all subarrays
for (int i = 0; i < n; i++)
{
// Insert first element
// in map
hm.Add(arr[i], 1);
for (int j = i + 1; j < n; j++)
{
// Update frequency of current
// subarray in the Dictionary
if(hm.ContainsKey(arr[j]))
hm[arr[j]]++;
else
hm.Add(arr[j], 1);
bool flag = false;
// Check if at least one
// element occurs once
// in current subarray
foreach (int k in hm.Values)
{
if (k == 1)
{
flag = true;
break;
}
}
// If any subarray doesn't
// have unique element
if (!flag)
return "No";
}
// Clear map for next
// subarray
hm.Clear();
}
// Return Yes if all subarray
// having at least 1 unique
// element
return "Yes";
}
// Driver Code
public static void Main(String[] args)
{
// Given array []arr
int[] arr = {1, 2, 1};
int N = arr.Length;
// Function Call
Console.WriteLine(check(arr, N));
}
}
// This code is contributed by Rajput-Ji
<script>
// Javascript program for above approach
// Function to check if all subarrays
// of array have at least one unique element
function check(arr, n)
{
// Stores frequency of subarray
// elements
var hm = new Map();
// Generate all subarrays
for(var i = 0; i < n; i++)
{
// Insert first element in map
hm.set(arr[i], 1);
for(var j = i + 1; j < n; j++)
{
// Update frequency of current
// subarray in the HashMap
if(hm.has(arr[j]))
hm.set(arr[j], hm.get(arr[j])+1);
else
hm.set(arr[j], 1)
var flag = false;
// Check if at least one element
// occurs once in current subarray
hm.forEach((value, key) => {
if (value == 1)
{
flag = true;
}
});
// If any subarray doesn't
// have unique element
if (!flag)
return "No";
}
// Clear map for next subarray
hm = new Map();
}
// Return Yes if all subarray
// having at least 1 unique element
return "Yes";
}
// Driver Code
// Given array arr[]
var arr = [1, 2, 1];
var N = arr.length;
// Function Call
document.write( check(arr, N));
</script>
Time Complexity: O(N3)
Auxiliary Space: O(N)
Efficient Approach: Follow the steps below to optimize the above approach:
- Iterate a loop over the range [0, N - 1] and create a map to store the frequency of each character present in the current subarray.
- Create a variable count to check that subarray has at least one element with frequency 1 or not.
- Traverse the array arr[] and update the frequency of each element in the map and update the count as:
- If the frequency of element is 1 then increment the count.
- If the frequency of element is 2 then decrement the count.
- In the above steps, if the value of count is 0, then print "No" as there exists a subarray who doesn't have any unique element in it.
- After all the iteration if the value of count is always positive, then print "Yes".
Below is the implementation of the above approach:
C++
// C++ program for the above approach
#include<bits/stdc++.h>
using namespace std;
// Function to check if all subarrays
// have at least one unique element
string check(int arr[], int n)
{
// Generate all subarray
for(int i = 0; i < n; i++)
{
// Store frequency of
// subarray's elements
map<int, int> hm;
int count = 0;
// Traverse the array over
// the range [i, N]
for(int j = i; j < n; j++)
{
// Update frequency of
// current subarray in map
hm[arr[j]]++;
// Increment count
if (hm[arr[j]] == 1)
count++;
// Decrement count
if (hm[arr[j]] == 2)
count--;
if (count == 0)
return "No";
}
}
// If all subarrays have at
// least 1 unique element
return "Yes";
}
// Driver Code
int main()
{
// Given array arr[]
int arr[] = { 1, 2, 1 };
int N = sizeof(arr) / sizeof(arr[0]);
// Function Call
cout << check(arr, N);
}
// This code is contributed by SURENDRA_GANGWAR
// Java program for the above approach
import java.util.*;
import java.lang.*;
class GFG {
// Function to check if all subarrays
// have at least one unique element
static String check(int arr[], int n)
{
// Generate all subarray
for (int i = 0; i < n; i++) {
// Store frequency of
// subarray's elements
Map<Integer, Integer> hm
= new HashMap<>();
int count = 0;
// Traverse the array over
// the range [i, N]
for (int j = i; j < n; j++) {
// Update frequency of
// current subarray in map
hm.put(arr[j],
hm.getOrDefault(arr[j], 0) + 1);
// Increment count
if (hm.get(arr[j]) == 1)
count++;
// Decrement count
if (hm.get(arr[j]) == 2)
count--;
if (count == 0)
return "No";
}
}
// If all subarrays have at
// least 1 unique element
return "Yes";
}
// Driver Code
public static void main(String[] args)
{
// Given array arr[]
int[] arr = { 1, 2, 1 };
int N = arr.length;
// Function Call
System.out.println(check(arr, N));
}
}
# Python3 program for the above approach
# Function to check if all subarrays
# have at least one unique element
def check(arr, n):
# Generate all subarray
for i in range(n):
# Store frequency of
# subarray's elements
hm = {}
count = 0
# Traverse the array over
# the range [i, N]
for j in range(i, n):
# Update frequency of
# current subarray in map
hm[arr[j]] = hm.get(arr[j], 0) + 1
# Increment count
if (hm[arr[j]] == 1):
count += 1
# Decrement count
if (hm[arr[j]] == 2):
count -= 1
if (count == 0):
return "No"
# If all subarrays have at
# least 1 unique element
return "Yes"
# Driver Code
if __name__ == '__main__':
# Given array arr[]
arr = [ 1, 2, 1 ]
N = len(arr)
# Function Call
print(check(arr, N))
# This code is contributed by mohit kumar 29
// C# program for the
// above approach
using System;
using System.Collections.Generic;
class GFG {
// Function to check if all
// subarrays have at least
// one unique element
static String check(int []arr,
int n)
{
// Generate all subarray
for (int i = 0; i < n; i++)
{
// Store frequency of
// subarray's elements
Dictionary<int,
int> hm =
new Dictionary<int,
int>();
int count = 0;
// Traverse the array over
// the range [i, N]
for (int j = i; j < n; j++)
{
// Update frequency of
// current subarray in map
if(hm.ContainsKey((arr[j])))
hm[arr[j]]++;
else
hm.Add(arr[j], 1);
// Increment count
if (hm[arr[j]] == 1)
count++;
// Decrement count
if (hm[arr[j]] == 2)
count--;
if (count == 0)
return "No";
}
}
// If all subarrays have at
// least 1 unique element
return "Yes";
}
// Driver Code
public static void Main(String[] args)
{
// Given array []arr
int[] arr = {1, 2, 1};
int N = arr.Length;
// Function Call
Console.WriteLine(check(arr, N));
}
}
// This code is contributed by gauravrajput1
<script>
//Javascript program for the above approach
// Function to check if all subarrays
// have at least one unique element
function check(arr, n)
{
// Generate all subarray
for(var i = 0; i < n; i++)
{
// Store frequency of
// subarray's elements
//map<int, int> hm;
var hm= new Map();
var count = 0;
// Traverse the array over
// the range [i, N]
for(var j = i; j < n; j++)
{
// Update frequency of
// current subarray in map
//hm[arr[j]]++;
if(hm.has(arr[j]))
hm.set(arr[j], hm.get(arr[j])+1)
else
hm.set(arr[j], 1)
// Increment count
if (hm.get(arr[j])==1)
count++;
// Decrement count
if (hm.get(arr[j]) == 2)
count--;
if (count == 0)
return "No";
}
}
// If all subarrays have at
// least 1 unique element
return "Yes";
}
var arr = [ 1, 2, 1 ];
var N = arr.length;
// Function Call
document.write(check(arr, N));
// This code is contributed by SoumikMondal
</script>
Time Complexity: O(N2)
Auxiliary Space: O(N)
Related Topic: Subarrays, Subsequences, and Subsets in Array
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