C# 递归代码

public class Solution {
    public bool CanReach(int[] arr, int start) {
        return Reach(arr, start, new bool[arr.Length]);
    }

    private bool Reach(int[] arr, int start, bool[] used){
        if (start < 0 || start >= arr.Length || used[start]) return false;
        if (arr[start] == 0) return true;
        used[start] = true;
        bool left = Reach(arr, start - arr[start], used);
        bool right = Reach(arr, start + arr[start], used);
        return left || right;
    }
}

C# 迭代代码

public class Solution {
    public bool CanReach(int[] arr, int start) {
        int n = arr.Length;
        bool[] used = new bool[n];
        Queue<int> queue = new Queue<int>();
        queue.Enqueue(start);
        while (queue.Count > 0){
            int current = queue.Dequeue();
            if (arr[current] == 0) return true;

            if ((current + arr[current]) < n && !used[current + arr[current]]){
                queue.Enqueue(current + arr[current]);
                used[current + arr[current]] = true;
            }

            if ((current - arr[current]) >= 0 && !used[current - arr[current]]){
                queue.Enqueue(current - arr[current]);
                used[current - arr[current]] = true;
            }
        }

        return false;
    }
}