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55. Jump Game
Medium
You are given an integer array nums. You are initially positioned at the array’s first index, and each element in the array represents your maximum jump length at that position.
Return true if you can reach the last index, or false otherwise.
Example 1:
Input: nums = [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: nums = [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.
Constraints:
1 <= nums.length <= 1040 <= nums[i] <= 105
Solution
# @param {Integer[]} nums
# @return {Boolean}
def can_jump(nums)
sz = nums.length
# We set 1 so it won't break on the first iteration
tmp = 1
(0...sz).each do |i|
# We always deduct tmp for every iteration
tmp -= 1
return false if tmp < 0
# Get the maximum value because this value is supposed
# to be our iterator. If both values are 0, then the next
# iteration we will return false.
# We can stop the whole iteration with this condition. Without this condition, the code
# runs in 2ms (79.6%). Adding this condition improves the performance to 1ms (100%)
# because if the test case jump value is quite large, instead of just iterating, we can
# just check using this condition.
# Example: [10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] -> we can just jump to the end without
# iterating the whole array.
tmp = [tmp, nums[i]].max
return true if i + tmp >= sz - 1
end
# We can just return true at the end because if tmp is 0 on the previous
# iteration,
# even though the next iteration index is the last one, it will return false under the
# tmp < 0 condition.
true
end