# Basic comprehension
squares = [x**2 for x in range(5)]  # [0, 1, 4, 9, 16]

# With condition
evens = [x for x in range(10) if x % 2 == 0]  # [0, 2, 4, 6, 8]

# Nested with transformation
matrix = [[1, 2], [3, 4]]
flattened = [num for row in matrix for num in row]  # [1, 2, 3, 4]

# Equivalent to loop (interview comparison)
result = []
for x in range(5):
    result.append(x**2)
# result = [0, 1, 4, 9, 16]  # Same as first example

# Example: Solve "Find max in list" problem step-by-step
# Step 1: Understand - Input: list of nums; Output: max value; Constraints: empty list?

def find_max(numbers):
    if not numbers:  # Step 2: Handle edge case (empty list)
        return None  # Or raise ValueError

    max_val = numbers  # Step 3: Initialize with first element
    for num in numbers[1:]:  # Step 4: Loop through rest (sub-problem: compare)
        if num > max_val:
            max_val = num
    return max_val  # Step 5: Return result

# Step 6: Test cases
print(find_max([3, 1, 4, 1, 5]))  # Output: 5
print(find_max([]))  # Output: None
print(find_max())  # Output: 10

# If stuck: Comment code to trace, or simplify (e.g., use max() built-in first to verify)

# Basic for loop over iterable (list)
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:  # Iterates each element directly
    print(fruit)      # Output: apple \n banana \n cherry

# For loop with range() for numeric sequences
for i in range(3):    # Generates 0, 1, 2 (start=0, stop=3, step=1)
    print(i)          # Output: 0 \n 1 \n 2

for i in range(1, 6, 2):  # Start=1, stop=6, step=2
    print(i)              # Output: 1 \n 3 \n 5

# Index-aware with enumerate() (gets both index and value)
for index, fruit in enumerate(fruits, start=1):  # start=1 for 1-based indexing
    print(f"{index}: {fruit}")                   # Output: 1: apple \n 2: banana \n 3: cherry

# Parallel iteration with zip() (pairs multiple iterables)
names = ["Alice", "Bob", "Charlie"]
ages = [25, 30, 35]
for name, age in zip(names, ages):  # Stops at shortest iterable
    print(f"{name} is {age} years old")  # Output: Alice is 25 years old \n Bob is 30 years old \n Charlie is 35 years old

# Nested for loops (outer for rows, inner for columns; e.g., matrix)
matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:         # Outer: each sublist
    for num in row:        # Inner: each element in row
        print(num, end=' ')  # Output: 1 2 3 4 5 6 7 8 9 (space-separated)

# For loop in list comprehension (concise iteration with optional condition)
squares = [x**2 for x in range(5)]  # Basic comprehension
print(squares)  # Output: [0, 1, 4, 9, 16]

evens_squared = [x**2 for x in range(10) if x % 2 == 0]  # With condition (if)
print(evens_squared)  # Output: [0, 4, 16, 36, 64]

# Nested comprehension (flattens 2D list)
flattened = [num for row in matrix for num in row]  # Equivalent to nested for
print(flattened)  # Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]