Check if an Array is Sorted
Last Updated :
13 May, 2025
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
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.
C++
#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;
}
// 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");
}
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.
C++
#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");
}
Time Complexity: O(n)
Auxiliary Space: O(n) for Recursion Call Stack.
Similar Reads
DSA Tutorial - Learn Data Structures and Algorithms DSA (Data Structures and Algorithms) is the study of organizing data efficiently using data structures like arrays, stacks, and trees, paired with step-by-step procedures (or algorithms) to solve problems effectively. Data structures manage how data is stored and accessed, while algorithms focus on
7 min read
Quick Sort QuickSort is a sorting algorithm based on the Divide and Conquer that picks an element as a pivot and partitions the given array around the picked pivot by placing the pivot in its correct position in the sorted array. It works on the principle of divide and conquer, breaking down the problem into s
12 min read
Merge Sort - Data Structure and Algorithms Tutorials Merge sort is a popular sorting algorithm known for its efficiency and stability. It follows the divide-and-conquer approach. It works by recursively dividing the input array into two halves, recursively sorting the two halves and finally merging them back together to obtain the sorted array. Merge
14 min read
Data Structures Tutorial Data structures are the fundamental building blocks of computer programming. They define how data is organized, stored, and manipulated within a program. Understanding data structures is very important for developing efficient and effective algorithms. What is Data Structure?A data structure is a st
2 min read
Bubble Sort Algorithm Bubble Sort is the simplest sorting algorithm that works by repeatedly swapping the adjacent elements if they are in the wrong order. This algorithm is not suitable for large data sets as its average and worst-case time complexity are quite high.We sort the array using multiple passes. After the fir
8 min read
Breadth First Search or BFS for a Graph Given a undirected graph represented by an adjacency list adj, where each adj[i] represents the list of vertices connected to vertex i. Perform a Breadth First Search (BFS) traversal starting from vertex 0, visiting vertices from left to right according to the adjacency list, and return a list conta
15+ min read
Binary Search Algorithm - Iterative and Recursive Implementation Binary Search Algorithm is a searching algorithm used in a sorted array by repeatedly dividing the search interval in half. The idea of binary search is to use the information that the array is sorted and reduce the time complexity to O(log N). Binary Search AlgorithmConditions to apply Binary Searc
15 min read
Insertion Sort Algorithm Insertion sort is a simple sorting algorithm that works by iteratively inserting each element of an unsorted list into its correct position in a sorted portion of the list. It is like sorting playing cards in your hands. You split the cards into two groups: the sorted cards and the unsorted cards. T
9 min read
Array Data Structure Guide In this article, we introduce array, implementation in different popular languages, its basic operations and commonly seen problems / interview questions. An array stores items (in case of C/C++ and Java Primitive Arrays) or their references (in case of Python, JS, Java Non-Primitive) at contiguous
4 min read
Sorting Algorithms A Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
3 min read