Merge dictionaries by summing matching values

Summary

Combine multiple dictionaries into one by summing values for matching keys.

Problem statement

Given a list of dictionaries where each dictionary maps keys to numeric values, merge them into a single dictionary. If a key appears in multiple dictionaries, its final value should be the sum of all values seen for that key. Preserve the insertion order based on the first time a key is encountered while processing the input list from left to right.

Task

Implement a function that merges a list of dictionaries by summing values that share the same key, preserving the order in which keys first appear.

Examples

Input format

A list of dictionaries. Example: [{'a':1}, {'b':2, 'a':3}]

Output format

A single dictionary with keys from all input dictionaries and summed numeric values for duplicate keys.

Constraints

- Input is a list (possibly empty) of dictionaries with numeric values. - Return an empty dictionary for an empty input list. - Preserve key order based on first appearance while iterating left-to-right through the list.

Samples