Program to check we can reach end of list by starting from k in Python

Suppose we have a list of numbers called nums and another number k. If we start at index k and at any index i, we can go either left or right by exactly nums[i] number of steps. We have to check whether we can reach the end of the list or not.

So, if the input is like nums = [0, 0, 2, 1, 3, 3, 1, 1] k = 2, then the output will be True, as if we start at index 2, then jump to index 4 and then jump to the last index 7.

To solve this, we will follow these steps−

• n:= size of nums

• visited := a list of size n and fill with 0

• tovisit := a list of size 1, and insert k into it

• while size of tovisit < 0, do

  • i:= last element from tovisit and delete it from tovisit

  • if i is same as n-1, then

  • return True

• if visited[i] is not same as 1, then

  • visited[i]:= 1

  • up:= i + nums[i]

  • down:= i - nums[i]

  • if up < n, then

  • insert up at the end of tovisit

  • if down >= 0, then

  • insert down at the end of tovisit

• return False

Let us see the following implementation to get better understanding−

Example

 Live Demo

class Solution:
   def solve(self, nums, k):
      n=len(nums)
      visited = [0]*n
      tovisit = [k]
      while len(tovisit)>0:
         i=tovisit.pop()
         if i==n-1:
            return True
         if visited[i]!=1:
            visited[i]=1
            up=i+nums[i]
            dn=i-nums[i]
         if up=0:
            tovisit.append(dn)
      return False
ob = Solution()
nums = [0, 0, 2, 1, 3, 3, 1, 1]
k = 2
print(ob.solve(nums, k))

Input

[0, 0, 2, 1, 3, 3, 1, 1], 2

Output

True