How do you solve Time Needed to Inform All Employees on LeetCode?

Time Needed to Inform All Employees (LeetCode #1376) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding tree structures is crucial for solving hierarchical problems.

What is the brute force solution for Time Needed to Inform All Employees?

The brute force approach for Time Needed to Inform All Employees is Brute Force, with O(n²) time complexity and O(1) space complexity. In the brute-force approach, we can simulate the process of informing each employee recursively. For each employee, we will calculate the total time taken to inform all their subordinates by recursively summing the inform times of each subordinate. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Time Needed to Inform All Employees?

Time Needed to Inform All Employees uses the following concepts: Tree, Depth-First Search, Breadth-First Search. The recommended patterns to study are: Tree Traversal, Depth-First Search, Breadth-First Search.

What are the interview tips for Time Needed to Inform All Employees?

Clarify the tree structure and relationships before coding. Think about edge cases, like when there's only one employee. Explain your thought process clearly while coding.

What are common mistakes when solving Time Needed to Inform All Employees?

Not considering all subordinates when calculating inform time. Confusing the order of operations in recursive calls.

#1376

Time Needed to Inform All Employees

Medium

TreeDepth-First SearchBreadth-First SearchTree TraversalDepth-First SearchBreadth-First Search

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

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Intuition

Time O(n)Space O(n)

In the optimal approach, we can use a depth-first search (DFS) or breadth-first search (BFS) to traverse the tree structure of employees. We will calculate the total time needed to inform all employees by keeping track of the maximum time taken by any subordinate.

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Algorithm

3 steps

1Step 1: Create an adjacency list to represent the tree structure of employees.
2Step 2: Use DFS or BFS to traverse the tree starting from the headID.
3Step 3: For each employee, calculate the total time as the inform time plus the maximum time from their subordinates.

solution.py14 lines

1# Full working Python code
2class Solution:
3    def numOfMinutes(self, n: int, headID: int, manager: List[int], informTime: List[int]) -> int:
4        from collections import defaultdict
5        tree = defaultdict(list)
6        for i in range(n):
7            if manager[i] != -1:
8                tree[manager[i]].append(i)
9        def dfs(emp):
10            max_time = 0
11            for sub in tree[emp]:
12                max_time = max(max_time, dfs(sub))
13            return max_time + informTime[emp]
14        return dfs(headID)

ℹ

Complexity note: The time complexity is linear because we visit each employee exactly once. The space complexity is also linear due to the storage of the tree structure.

1Understanding tree structures is crucial for solving hierarchical problems.
2Recursion is a powerful tool for traversing trees.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.