old_contents: """Leetcode 55. Jump Game
  Medium
  
  URL: https://leetcode.com/problems/jump-game/
  
  Given an array of non-negative integers, you are initially positioned at the 
  first index of the array.
  
  Each element in the array represents your maximum jump length at that position.
  
  Determine if you are able to reach the last index.
  
  Example 1:
  Input: [2,3,1,1,4]
  Output: true
  Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
  
  Example 2:
  Input: [3,2,1,0,4]
  Output: false
  Explanation: You will always arrive at index 3 no matter what. Its maximum
  jump length is 0, which makes it impossible to reach the last index.
  """
  
  class Solution(object):
      def canJump(self, nums):
          """
          :type nums: List[int]
          :rtype: bool
  
          Time complexity: O(n).
          Space complexity: O(1).
          """
          # Memorize max reachable index by end.
          end = 0
  
          for i in range(len(nums)):
              if i > end:
                  # Position i is not reachable.
                  return False
  
              # Update end by checking i + nums[i] > end.
              end = max(end, i + nums[i])
  
          return True
  
  
  def main():
      # Ans: True
      nums = [2,3,1,1,4]
      print Solution().canJump(nums)
  
      # Ans: False
      nums = [3,2,1,0,4]
      print Solution().canJump(nums)
  
  
  if __name__ == '__main__':
      main()
  
new_contents: """Leetcode 55. Jump Game
  Medium
  
  URL: https://leetcode.com/problems/jump-game/
  
  Given an array of non-negative integers, you are initially positioned at the 
  first index of the array.
  
  Each element in the array represents your maximum jump length at that position.
  
  Determine if you are able to reach the last index.
  
  Example 1:
  Input: [2,3,1,1,4]
  Output: true
  Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
  
  Example 2:
  Input: [3,2,1,0,4]
  Output: false
  Explanation: You will always arrive at index 3 no matter what. Its maximum
  jump length is 0, which makes it impossible to reach the last index.
  """
  
  class SolutionGreedy(object):
      def canJump(self, nums):
          """
          :type nums: List[int]
          :rtype: bool
  
          Time complexity: O(n).
          Space complexity: O(1).
          """
          # Update max reachable index by end.
          end = 0
  
          for i in range(len(nums)):
              # Index i is not reachable.
              if end < i:
                  return False
  
              # Update end by checking i + nums[i] > end.
              end = max(end, i + nums[i])
  
          return True
  
  
  def main():
      # Ans: True
      nums = [2,3,1,1,4]
      print SolutionGreedy().canJump(nums)
  
      # Ans: False
      nums = [3,2,1,0,4]
      print SolutionGreedy().canJump(nums)
  
  
  if __name__ == '__main__':
      main()
  
subject: Enhance comments