Reference library

Dictionaries & sets

Key–value maps, uniqueness, counting, grouping, and fast lookups.

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Dictionaries & sets easy

Check Invertible Mapping for Duplicate Values in Python

Detect duplicate values among (key, value) pairs to ensure the mapping is invertible, using a dictionary for O(1) lookups.

dictionary mapping duplicate-check
Python 
def invertible_after_dedup(pairs):
    """
    Check whether a set of (key, value) pairs is invertible,
    i.e., no duplicate values exist for different keys.
    """
    seen = {}
    for key, value in pairs:
        if value in seen and seen[value] != key:
            return False, f"Duplicate value '{value}' for k…
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