README.md

1306. Jump Game III

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

Solutions (Ruby)

1. Solution

# @param {Integer[]} arr
# @param {Integer} start
# @return {Boolean}
def can_reach(arr, start)
    positions = [start]

    while not positions.empty?
        i = positions.pop

        return true if arr[i] == 0

        if arr[i] > 0
            positions.push(i + arr[i]) if i + arr[i] < arr.length
            positions.push(i - arr[i]) if i - arr[i] >= 0
            arr[i] = -arr[i]
        end
    end

    return false
end