Check if an Array is Sorted
Last Updated :
07 Mar, 2025
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Given an array of size n, the task is to check if it is sorted in ascending order or not. Equal values are allowed in an array and two consecutive equal values are considered sorted.
Examples:
Input: arr[] = [20, 21, 45, 89, 89, 90]
Output: Yes
Input: arr[] = [20, 20, 45, 89, 89, 90]
Output: Yes
Input: arr[] = [20, 20, 78, 98, 99, 97]
Output: No
Table of Content
Iterative approach – O(n) Time and O(1) Space
The idea is simple. We start traversing from the second element. For every element we check if it is smaller than or equal to previous element or not. At any point if we find previous element greater, we return false.
For example [10, 20, 30, 5, 6[
i = 1 : (10 <= 20), continue
i = 2 : (20 <= 30), continue
i = 3 : (30 > 5), return false.
#include <bits/stdc++.h>
using namespace std;
// Function that returns true if vector is
// sorted in non-decreasing order.
bool isSorted(const vector<int>& arr)
{
// For an array to be sorted, every
// element must be greater than the
// previous element
for (int i = 1; i < arr.size(); i++)
if (arr[i - 1] > arr[i])
return false;
return true;
}
// Driver code
int main()
{
vector<int> arr = { 20, 23, 23, 45, 78, 88 };
cout << (isSorted(arr) ? "Yes\n" : "No\n");
return 0;
}
cout << (isSorted(arr) ? "Yes\n" : "No\n");
return 0;
}
// C program to check if an
// Array is sorted or not
#include <stdio.h>
// Function that returns true if array is
// sorted in non-decreasing order.
int arraySortedOrNot(int arr[], int n)
{
// Array has one or no element
if (n == 0 || n == 1)
return 1;
for (int i = 1; i < n; i++) {
// Unsorted pair found
if (arr[i - 1] > arr[i])
return 0;
}
// No unsorted pair found
return 1;
}
// Driver code
int main()
{
int arr[] = { 20, 23, 23, 45, 78, 88 };
int n = sizeof(arr) / sizeof(arr[0]);
if (arraySortedOrNot(arr, n))
printf("Yes\n");
else
printf("No\n");
return 0;
}
// Recursive approach to check if an
// Array is sorted or not
class GFG {
// Function that returns true if array is
// sorted in non-decreasing order.
static boolean arraySortedOrNot(int arr[], int n)
{
// Array has one or no element
if (n == 0 || n == 1)
return true;
for (int i = 1; i < n; i++)
// Unsorted pair found
if (arr[i - 1] > arr[i])
return false;
// No unsorted pair found
return true;
}
// driver code
public static void main(String[] args)
{
int arr[] = { 20, 23, 23, 45, 78, 88 };
int n = arr.length;
if (arraySortedOrNot(arr, n))
System.out.print("Yes\n");
else
System.out.print("No\n");
}
}
// This code is contributed by Anant Agarwal.
# Python3 program to check if an
# Array is sorted or not
# Function that returns true if array is
# sorted in non-decreasing order.
def arraySortedOrNot(arr, n):
# Array has one or no element
if (n == 0 or n == 1):
return True
for i in range(1, n):
# Unsorted pair found
if (arr[i-1] > arr[i]):
return False
# No unsorted pair found
return True
# Driver code
arr = [20, 23, 23, 45, 78, 88]
n = len(arr)
if (arraySortedOrNot(arr, n)):
print("Yes")
else:
print("No")
# This code is contributed by Anant Agarwal.
// Recursive approach to check if an
// Array is sorted or not
using System;
class GFG
{
// Function that returns true if array is
// sorted in non-decreasing order.
static bool arraySortedOrNot(int []arr, int n)
{
// Array has one or no element
if (n == 0 || n == 1)
return true;
for (int i = 1; i < n; i++)
// Unsorted pair found
if (arr[i - 1] > arr[i])
return false;
// No unsorted pair found
return true;
}
// Driver code
public static void Main(String[] args)
{
int []arr = { 20, 23, 23, 45, 78, 88 };
int n = arr.Length;
if (arraySortedOrNot(arr, n))
Console.Write("Yes\n");
else
Console.Write("No\n");
}
}
// This code is contributed by PrinciRaj1992
// JavaScript program Iterative approach to check if an
// Array is sorted or not
// Function that returns true if array is
// sorted in non-decreasing order.
function arraySortedOrNot(arr, n)
// Array has one or no element
if (n === 0 || n === 1) {
return true;
}
for (let i = 1; i < n; i++) {
// Unsorted pair found
if (arr[i - 1] > arr[i]) {
return false;
}
}
// No unsorted pair found
return true;
}
// Driver Code
let arr = [20, 23, 23, 45, 78, 88];
let n = arr.length;
if (arraySortedOrNot(arr, n)) {
console.log("Yes");
} else {
console.log("No");
}
Output
Yes
Recursive approach – O(n) Time and O(n) Space
The basic idea for the recursive approach:
- If size of array is zero or one, return true.
- Check last two elements of array, if they are sorted, perform a recursive call with n-1 else, return false.
#include <iostream>
#include <vector>
using namespace std;
// Recursive function that returns true if vector is
// sorted in non-decreasing order.
bool isSorted(const vector<int>& arr, int n)
{
// Base case
if (n == 1 || n == 0)
return true;
// Check if current and previous elements are in order
// and recursively check the rest of the array
return arr[n - 1] >= arr[n - 2] && isSorted(arr, n - 1);
}
// Driver code
int main()
{
vector<int> arr = { 20, 23, 23, 45, 78, 88 };
cout << (isSorted(arr, arr.size()) ? "Yes\n" : "No\n");
return 0;
}
// C Recursive approach to check if an
// Array is sorted or not
#include <stdio.h>
// Function that returns true if array is
// sorted in non-decreasing order.
int arraySortedOrNot(int a[], int n)
{
// Base case
if (n == 1 || n == 0) {
return 1;
}
// Check if present index and index
// previous to it are in correct order
// and rest of the array is also sorted
// if true then return true else return
// false
return a[n - 1] >= a[n - 2]
&& arraySortedOrNot(a, n - 1);
}
// Driver code
int main()
{
int arr[] = { 20, 23, 23, 45, 78, 88 };
int n = sizeof(arr) / sizeof(arr[0]);
// Function Call
if (arraySortedOrNot(arr, n)) {
printf("Yes\n");
}
else {
printf("No\n");
}
return 0;
}
// Java Recursive approach to check if an
// Array is sorted or not
class GFG {
// Function that returns true if array is
// sorted in non-decreasing order.
static boolean arraySortedOrNot(int a[], int n)
{
// base case
if (n == 1 || n == 0)
return true;
// check if present index and index
// previous to it are in correct order
// and rest of the array is also sorted
// if true then return true else return
// false
return a[n - 1] >= a[n - 2]
&& arraySortedOrNot(a, n - 1);
}
// Driver code
public static void main(String[] args)
{
int arr[] = { 20, 23, 23, 45, 78, 88 };
int n = arr.length;
// Function Call
if (arraySortedOrNot(arr, n))
System.out.print("Yes");
else
System.out.print("No");
}
}
// This code is contributed by Durgesh N. Birmiwal.
# Python3 recursive program to check
# if an Array is sorted or not
# Function that returns true if array
# is sorted in non-decreasing order.
def arraySortedOrNot(arr, n):
# Base case
if (n == 0 or n == 1):
return True
# Check if present index and index
# previous to it are in correct order
# and rest of the array is also sorted
# if true then return true else return
# false
return (arr[n - 1] >= arr[n - 2] and
arraySortedOrNot(arr, n - 1))
# Driver code
arr = [ 20, 23, 23, 45, 78, 88 ]
n = len(arr)
# Function Call
if (arraySortedOrNot(arr, n)):
print("Yes")
else:
print("No")
# This code is contributed by Virusbuddah
// C# recursive approach to check if an
// Array is sorted or not
using System;
class GFG{
// Function that returns true if array is
// sorted in non-decreasing order.
static bool arraySortedOrNot(int[] a, int n)
{
// Base case
if (n == 1 || n == 0)
{
return true;
}
// Check if present index and index
// previous to it are in correct order
// and rest of the array is also sorted
// if true then return true else return
// false
return a[n - 1] >= a[n - 2] &&
arraySortedOrNot(a, n - 1);
}
// Driver code
static public void Main()
{
int[] arr = { 20, 23, 23, 45, 78, 88 };
int n = arr.Length;
// Function Call
if (arraySortedOrNot(arr, n))
{
Console.WriteLine("Yes");
}
else
{
Console.WriteLine("No");
}
}
}
// This code is contributed by rag2127
// JavaScript Recursive approach to check if an
// Array is sorted or not
// Function that returns true if array is
// sorted in non-decreasing order.
function arraySortedOrNot(a, n) {
// Base case
if (n == 1 || n == 0) {
return true;
}
// Check if present index and index
// previous to it are in correct order
// and rest of the array is also sorted
// if true then return true else return
// false
return a[n - 1] >= a[n - 2] && arraySortedOrNot(a, n - 1);
}
// Driver code
let arr = [20, 23, 23, 45, 78, 88];
let n = arr.length;
// Function Call
if (arraySortedOrNot(arr, n)) {
console.log("Yes");
} else {
console.log("No");
}
Output
Yes
Time Complexity: O(n)
Auxiliary Space: O(n) for Recursion Call Stack.
