Approach #1: DepthFirst Search [Accepted]
Intuition and Algorithm
Let's use a hashmap emap = {employee.id > employee}
to query employees quickly.
Now to find the total importance of an employee, it will be the importance of that employee, plus the total importance of each of that employee's subordinates. This is a straightforward depthfirst search.
Complexity Analysis

Time Complexity: , where is the number of employees. We might query each employee in
dfs
. 
Space Complexity: , the size of the implicit call stack when evaluating
dfs
.
Analysis written by: @awice.