Write Python code to count word frequency in a string.

Here is a clean implementation:

def count_word_freq(input_string):
    frequency = {}
    words = input_string.split()
    for word in words:
        frequency[word] = frequency.get(word, 0) + 1
    return frequency

Explanation:

• split() breaks the string on whitespace.
• frequency.get(word, 0) returns the current count or 0 if the word is new.
• Complexity is O(n) where n is the number of words; space complexity is O(k) for k unique words.