Jump Game 3, BFS Approach

Standard problem for a BFS: https://leetcode.com/problems/jump-game-iii/

1306. Jump Game III

Medium

Given an array of non-negative integers arr, you are initially positioned at start index of the array. When you are at index i, you can jump to i + arr[i] or i - arr[i], check if you can reach to any index with value 0.

Notice that you can not jump outside of the array at any time.

Example 1:

Input: arr = [4,2,3,0,3,1,2], start = 5
Output: true
Explanation: 
All possible ways to reach at index 3 with value 0 are: 
index 5 -> index 4 -> index 1 -> index 3 
index 5 -> index 6 -> index 4 -> index 1 -> index 3 

Example 2:

Input: arr = [4,2,3,0,3,1,2], start = 0
Output: true 
Explanation: 
One possible way to reach at index 3 with value 0 is: 
index 0 -> index 4 -> index 1 -> index 3

Example 3:

Input: arr = [3,0,2,1,2], start = 2
Output: false
Explanation: There is no way to reach at index 1 with value 0.

Constraints:

• 1 <= arr.length <= 5 * 10^4
• 0 <= arr[i] < arr.length
• 0 <= start < arr.length

One way to solve it is via Breadth-First-Search, or BFS. Enqueue the initial position, make sure to mark it as visited. Start the processing. If the solution is found, return. Otherwise emqueue if not visited. Very straightforward; slow, but does the trick. Code is down below, cheers, ACC.

public class Solution

{

    public bool CanReach(int[] arr, int start)

    {

        Queue<int> queueIndex = new Queue<int>();

        Hashtable visited = new Hashtable();

        visited.Add(start, true);

        queueIndex.Enqueue(start);

        while (queueIndex.Count > 0)

        {

            int current = queueIndex.Dequeue();

            if (arr[current] == 0) return true;

            int[] candidates = { current + arr[current], current - arr[current] };

            foreach(int candidate in candidates)

            {

                if (candidate >= 0 && candidate < arr.Length && !visited.ContainsKey(candidate))

                {

                    visited.Add(candidate, true);

                    queueIndex.Enqueue(candidate);

                }

            }

        }

        return false;

    }

}