Arrays

# Python मध्ये list = dynamic array
arr = [5, 2, 8, 1, 9, 3]

# Access — O(1)
print(arr[0])   # 5
print(arr[-1])  # 3 (last element)

# Insert at end — O(1)
arr.append(7)

# Insert at index — O(n)
arr.insert(2, 99)

# Delete — O(n)
arr.remove(8)   # value ने
arr.pop(0)      # index ने

# Length
print(len(arr))

# Problem: sorted array मध्ये दोन numbers शोधा जे target ला add होतात
def two_sum_sorted(arr, target):
    left, right = 0, len(arr) - 1

    while left < right:
        current_sum = arr[left] + arr[right]
        if current_sum == target:
            return [left, right]
        elif current_sum < target:
            left += 1   # sum वाढवायला left पुढे
        else:
            right -= 1  # sum कमी करायला right मागे

    return []

arr = [1, 3, 5, 7, 9, 11]
print(two_sum_sorted(arr, 12))  # [1, 4] → 3+9=12

# Problem: k size च्या subarray चा maximum sum
def max_subarray_sum(arr, k):
    window_sum = sum(arr[:k])   # पहिली window
    max_sum = window_sum

    for i in range(k, len(arr)):
        window_sum += arr[i] - arr[i - k]   # window slide
        max_sum = max(max_sum, window_sum)

    return max_sum

arr = [2, 1, 5, 1, 3, 2]
print(max_subarray_sum(arr, 3))  # 9 (5+1+3)