Merge Nested Dictionaries Iteratively

Given a list of Python dictionaries, merge them into a single dictionary without using recursion.

Rules:

• Process the dictionaries from left to right.
• If a key appears in only one dictionary, keep that key-value pair.
• If the same key appears in multiple dictionaries:
• when both values are dictionaries, merge those dictionaries using the same rules;
• otherwise, the value from the later dictionary overrides the earlier one.
• You may assume keys are strings.

Example:

• Input:
• [{"a": 1, "b": {"x": 2}}, {"b": {"y": 3}, "c": 4}, {"b": {"x": 5}}]
• Output:
• {"a": 1, "b": {"x": 5, "y": 3}, "c": 4}

Implement a function that returns the merged dictionary using an iterative approach.