input: Write a python function to count the occurrences of each word in a sentence and return a dictionary with the word as the key and its count as the value.
  assert count_words('The quick brown fox jumps over the lazy dog') == {'The': 1, 'quick': 1, 'brown': 1, 'fox': 1, 'jumps': 1, 'over': 1, 'the': 1, 'lazy': 1, 'dog': 1}
  assert count_words('hello hello world') == {'hello': 2, 'world': 1}
  assert count_words('test test test test') == {'test': 4}
output: def count_words(sentence):
      words = sentence.split()
      word_count = {}
      for word in words:
          word_count[word] = word_count.get(word, 0) + 1
      return word_count