Write Python logic to count word frequency in a string.

You can solve this by splitting the string into words and using a dictionary or collections.Counter to tally occurrences. For example:

from collections import Counter

def word_frequency(text):
    # Normalize: lower case and split on whitespace
    words = text.lower().split()
    return Counter(words)

text = "Hello world hello"
print(word_frequency(text))  # Counter({'hello': 2, 'world': 1})

This runs in O(n) time where n is the number of words, and uses O(k) space for k unique words. If you need to handle punctuation, use regex or str.translate to strip punctuation before splitting.