Nästlade loopar och loopmönster

for i in range(3):
    for j in range(3):
        print(i, j)

for i in range(1, 4):
    for j in range(1, 4):
        print(f'{i*j:3}', end='')
    print()

for i in range(1, 6):
    print('*' * i)

matrix = [[1,2,3],[4,5,6]]
for row in matrix:
    for val in row:
        print(val, end=' ')
    print()

matrix = [[1,2],[3,4]]
total = sum(v for row in matrix for v in row)
print(total)

matrix = [[1,2,3],[4,5,6],[7,8,9]]
for i, row in enumerate(matrix):
    for j, val in enumerate(row):
        if val == 5:
            print(f'Found at ({i},{j})')

items = ['a','b','c']
for i in range(len(items)):
    for j in range(i+1, len(items)):
        print(items[i], items[j])

# Efficient: use a set for inner lookup
data = {1, 2, 3, 4}
result = [x for x in range(10) if x in data]  # O(n)
print(result)

matrix = [[1,2],[3,4]]
flat = [x for row in matrix for x in row]
print(flat)

def find_in_matrix(matrix, target):
    for i, row in enumerate(matrix):
        for j, val in enumerate(row):
            if val == target:
                return (i, j)
    return None
print(find_in_matrix([[1,2],[3,4]], 3))