Arrays & Basics (Easy)Master the fundamental array operations with these curated practice problems.

Find Maximum Element

Problem Statement

Given an array of integers, find the largest element present in the array.

Solution

def find_max(arr):
    if not arr:
        return None
    max_val = arr[0]
    for num in arr:
        if num > max_val:
            max_val = num
    return max_val

Find Minimum Element

Problem Statement

Given an array of integers, find the smallest element present in the array.

Solution

def find_min(arr):
    if not arr:
        return None
    min_val = arr[0]
    for num in arr:
        if num < min_val:
            min_val = num
    return min_val

Reverse an Array

Problem Statement

Reverse the order of elements in a given array in-place.

Solution

def reverse_array(arr):
    left, right = 0, len(arr) - 1
    while left < right:
        arr[left], arr[right] = arr[right], arr[left]
        left += 1
        right -= 1
    return arr

Check if Array is Sorted

Problem Statement

Verify whether the given array is sorted in non-decreasing order.

Solution

def is_sorted(arr):
    for i in range(len(arr) - 1):
        if arr[i] > arr[i+1]:
            return False
    return True

Count Frequency of Elements

Problem Statement

Find the number of occurrences of each distinct element in an array.

Solution

`def count_frequency(arr):
    frequency = {

Find Second Largest Element

Problem Statement

Given an array of integers, find the second largest element. Assume there are at least two distinct elements.

Solution

def find_second_largest(arr):
    if len(arr) < 2:
        return None
    first = second = float('-inf')
    for num in arr:
        if num > first:
            second = first
            first = num
        elif num > second and num != first:
            second = num
    return second if second != float('-inf') else None

Sum of Array Elements

Problem Statement

Calculate the sum of all elements in a given numeric array.

Solution

def array_sum(arr):
    total = 0
    for num in arr:
        total += num
    return total

Rotate Array by K Positions

Problem Statement

Rotate the array to the right by k steps, where k is non-negative.

Solution

def rotate_array(arr, k):
    n = len(arr)
    if n == 0: return arr
    k %= n
    
    def reverse(start, end):
        while start < end:
            arr[start], arr[end] = arr[end], arr[start]
            start += 1
            end -= 1
            
    reverse(0, n - 1)
    reverse(0, k - 1)
    reverse(k, n - 1)
    return arr

Remove Duplicates from Sorted Array

Problem Statement

Given a sorted array, remove duplicates in-place such that each element appears only once and return the new length.

Solution

def remove_duplicates(arr):
    if not arr: return 0
    i = 0
    for j in range(1, len(arr)):
        if arr[j] != arr[i]:
            i += 1
            arr[i] = arr[j]
    return i + 1

Find Missing Number

Problem Statement

Given an array containing n distinct numbers in the range [0, n], return the only number in the range that is missing.

Solution

def find_missing_number(arr):
    n = len(arr)
    expected_sum = n * (n + 1) // 2
    actual_sum = sum(arr)
    return expected_sum - actual_sum

Move All Zeros to End

Problem Statement

Given an array, move all 0's to the end while maintaining the relative order of non-zero elements.

Solution

def move_zeros(arr):
    pos = 0
    for i in range(len(arr)):
        if arr[i] != 0:
            arr[pos], arr[i] = arr[i], arr[pos]
            pos += 1
    return arr

Find Index of Element

Problem Statement

Find the index of the first occurrence of a target element in an array. Return -1 if not found.

Solution

def find_index(arr, target):
    for i in range(len(arr)):
        if arr[i] == target:
            return i
    return -1

Linear Search Implementation

Problem Statement

Implement the linear search algorithm to find if an element exists in an array.

Solution

def linear_search(arr, target):
    for element in arr:
        if element == target:
            return True
    return False

Count Even and Odd Numbers

Problem Statement

Return a count of even and odd integers present in the array.

Solution

`def count_even_odd(arr):
    even_count = 0
    odd_count = 0
    for num in arr:
        if num % 2 == 0:
            even_count += 1
        else:
            odd_count += 1
    return {"even": even_count, "odd": odd_count

Find Largest Pair Sum

Problem Statement

Find the maximum sum of any two elements in an array.

Solution

def largest_pair_sum(arr):
    if len(arr) < 2: return None
    max1 = max2 = float('-inf')
    for num in arr:
        if num > max1:
            max2 = max1
            max1 = num
        elif num > max2:
            max2 = num
    return max1 + max2

Merge Two Arrays

Problem Statement

Merge two sorted arrays into a single sorted array.

Solution

def merge_sorted_arrays(arr1, arr2):
    i = j = 0
    result = []
    while i < len(arr1) and j < len(arr2):
        if arr1[i] < arr2[j]:
            result.append(arr1[i])
            i += 1
        else:
            result.append(arr2[j])
            j += 1
    result.extend(arr1[i:])
    result.extend(arr2[j:])
    return result

Check Palindrome Array

Problem Statement

Determine if the given array is a palindrome (reads the same forward and backward).

Solution

def is_palindrome(arr):
    left, right = 0, len(arr) - 1
    while left < right:
        if arr[left] != arr[right]:
            return False
        left += 1
        right -= 1
    return True

Find Duplicate Element

Problem Statement

Find all duplicate elements in an array. Each duplicate should appear only once in the result.

Solution

def find_duplicates(arr):
    seen = set()
    duplicates = set()
    for num in arr:
        if num in seen:
            duplicates.add(num)
        else:
            seen.add(num)
    return list(duplicates)

Count Occurrences of a Number

Problem Statement

Find how many times a target number appears in an array.

Solution

def count_occurrences(arr, target):
    count = 0
    for num in arr:
        if num == target:
            count += 1
    return count

Find Intersection of Two Arrays

Problem Statement

Find the common elements present in two given arrays.

Solution

def find_intersection(arr1, arr2):
    set1 = set(arr1)
    set2 = set(arr2)
    return list(set1 & set2)

Find Union of Two Arrays

Problem Statement

Find the union of two arrays (all unique elements from both).

Solution

def find_union(arr1, arr2):
    return list(set(arr1) | set(arr2))

Replace Elements with Greatest on Right

Problem Statement

Replace every element in the array with the greatest element among the elements to its right, and replace the last element with -1.

Solution

def replace_elements(arr):
    n = len(arr)
    max_seen = -1
    for i in range(n - 1, -1, -1):
        temp = arr[i]
        arr[i] = max_seen
        if temp > max_seen:
            max_seen = temp
    return arr

Find Equilibrium Index

Problem Statement

Find the index where the sum of elements to its left equals the sum of elements to its right.

Solution

def equilibrium_index(arr):
    total_sum = sum(arr)
    left_sum = 0
    for i in range(len(arr)):
        right_sum = total_sum - left_sum - arr[i]
        if left_sum == right_sum:
            return i
        left_sum += arr[i]
    return -1

Prefix Sum Array

Problem Statement

Create a prefix sum array where each element at index i is the sum of elements from 0 to i.

Solution

def get_prefix_sum(arr):
    if not arr: return []
    prefix = [0] * len(arr)
    prefix[0] = arr[0]
    for i in range(1, len(arr)):
        prefix[i] = prefix[i-1] + arr[i]
    return prefix

Find Smallest Element

Problem Statement

Identify the minimum value in an array.

Solution

def find_min(arr):
    if not arr: return None
    min_val = arr[0]
    for num in arr:
        if num < min_val:
            min_val = num
    return min_val

Check if Array Contains Element

Problem Statement

Check if a specific element exists in the given array.

Solution

def contains_element(arr, target):
    for num in arr:
        if num == target:
            return True
    return False

Copy Array Elements

Problem Statement

Create a new array that is a copy of the original array.

Solution

def copy_array(arr):
    copy_arr = []
    for num in arr:
        copy_arr.append(num)
    return copy_arr

Find Difference Between Max and Min

Problem Statement

Calculate the difference between the maximum and minimum elements in an array.

Solution

def max_min_difference(arr):
    if not arr: return 0
    max_val = min_val = arr[0]
    for num in arr:
        if num > max_val: max_val = num
        if num < min_val: min_val = num
    return max_val - min_val

Check Array Rotation

Problem Statement

Check if an array is a rotated version of another array.

Solution

def is_rotated(arr1, arr2):
    if len(arr1) != len(arr2): return False
    # Simplified check using concatenation
    s1 = "".join(map(str, arr1))
    s2 = "".join(map(str, arr2))
    return s2 in (s1 + s1)

Left Rotate Array by One

Problem Statement

Shift all elements of the array to the left by one position in-place.

Solution

def left_rotate_one(arr):
    if not arr: return arr
    first = arr[0]
    for i in range(len(arr) - 1):
        arr[i] = arr[i+1]
    arr[len(arr)-1] = first
    return arr

Find Pair with Given Sum

Problem Statement

Find if there exists a pair of elements in the array whose sum equals a given target.

Solution

def find_pair_sum(arr, target):
    seen = set()
    for num in arr:
        complement = target - num
        if complement in seen:
            return (complement, num)
        seen.add(num)
    return None

Find Subarray with Sum Zero

Problem Statement

Return True if there is a subarray (continuous elements) whose sum is equal to zero.

Solution

`def has_zero_sum_subarray(arr):
    seen_sums = {0

Count Distinct Elements

Problem Statement

Calculate the number of unique elements in an array.

Solution

def count_distinct(arr):
    return len(set(arr))

Find First Repeating Element

Problem Statement

Find the first element in an array that repeats. Return the element or None.

Solution

def first_repeating(arr):
    seen = set()
    for num in arr:
        if num in seen:
            return num
        seen.add(num)
    return None

Find Last Occurrence

Problem Statement

Find the index of the last occurrence of a target element in an array.

Solution

def find_last_occurrence(arr, target):
    for i in range(len(arr) - 1, -1, -1):
        if arr[i] == target:
            return i
    return -1

Sum of Alternate Elements

Problem Statement

Calculate the sum of elements at even indices (0, 2, 4...) in an array.

Solution

def sum_alternate(arr):
    alt_sum = 0
    for i in range(0, len(arr), 2):
        alt_sum += arr[i]
    return alt_sum

Find Largest Three Elements

Problem Statement

Find the three largest distinct elements in an array.

Solution

def largest_three(arr):
    first = second = third = float('-inf')
    for num in arr:
        if num > first:
            third = second
            second = first
            first = num
        elif num > second and num != first:
            third = second
            second = num
        elif num > third and num != first and num != second:
            third = num
    return [first, second, third]

Check Monotonic Array

Problem Statement

Determine if an array is monotonic (either entirely non-increasing or entirely non-decreasing).

Solution

def is_monotonic(arr):
    increasing = decreasing = True
    for i in range(1, len(arr)):
        if arr[i] < arr[i-1]:
            increasing = False
        if arr[i] > arr[i-1]:
            decreasing = False
    return increasing or decreasing

Remove Specific Element

Problem Statement

Remove all occurrences of a specific element from the array in-place and return the new length.

Solution

def remove_element(arr, val):
    pos = 0
    for i in range(len(arr)):
        if arr[i] != val:
            arr[pos] = arr[i]
            pos += 1
    return pos

Find Majority Element (Basic)

Problem Statement

Find the element that appears more than n/2 times in an array of size n.

Solution

def find_majority(arr):
    candidate = None
    count = 0
    for num in arr:
        if count == 0:
            candidate = num
            count = 1
        elif num == candidate:
            count += 1
        else:
            count -= 1
    return candidate

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Arrays & Basics (Easy) / Find Maximum Element

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Find Maximum Element

Given an array of integers, find the largest element present in the array.

1
Initialize a variable (e.g., max_val) with the first element of the array.
2
Iterate through the array starting from the second element.
3
In each step, compare the current element with max_val.
4
If the current element is greater, update max_val.
5
After checking all elements, return the value stored in max_val.

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