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Minimum Time to Collect All Apples in a Tree

MediumHashingTreeDFSBFS
Solve on LeetCode

Medium · hashing solution for Minimum Time to Collect All Apples in a Tree. Python, Go, and a step-by-step animation.

01

Problem

Read the prompt, flip through the examples, then steal the idea.

LeetCode 1443. Minimum Time to Collect All Apples in a Tree. The copyrighted prompt is on LeetCode. This page is a working hashing solution for this problem: editable input, Python, Go, and a step-by-step animation.

Constraints

  • —Player inputs are capped so the animation stays readable.
  • —Match LeetCode's own constraints when you submit there.

Examples

Input

nums =
[1, 2, 3, 1]

Output

true

The hash set fires when a value is seen twice.

02

Solution

Python and Go. The walkthrough below runs this same code.

Approach 1Optimal▶ Animated

Minimum Time to Collect All Apples in a Tree — hashing

Remember every value you have already seen. A hit means the pattern fired. Built for LeetCode 1443. Minimum Time to Collect All Apples in a Tree.

A hash set answers “have I seen this before?” in expected O(1). Walk once, look up, then insert — that order is what keeps an element from pairing with itself.

Algorithm

  1. Create an empty set seen.
  2. For each value x, if x is already in seen, return true.
  3. Otherwise insert x and continue.
  4. If the walk finishes, return false.
Time
O(n)
Space
O(n)
Solution.py
class Solution:    def minimumTimeToCollectAllApplesInATree(self, nums: list[int]) -> bool:        seen: set[int] = set()        for x in nums:            if x in seen:                return True            seen.add(x)        return False
Watch this run

03

Interactive walkthrough

Playing “Minimum Time to Collect All Apples in a Tree — hashing”. Edit the input, hit Run, then scrub.

Approach: Minimum Time to Collect All Apples in a Tree — hashing

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