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
class Solution {
public boolean backtrack(int[] arr, int start, boolean[] visited) {
if (start < 0 || start >= visited.length || visited[start])
return false;
if (arr[start] == 0)
return true;
visited[start] = true;
boolean ans = backtrack(arr, start + arr[start], visited) || backtrack(arr, start - arr[start], visited);
visited[start] = false;
return ans;
}
public boolean canReach(int[] arr, int start) {
boolean[] visited = new boolean[arr.length];
return backtrack(arr, start, visited);
}
}