#1503
Last Moment Before All Ants Fall Out of a Plank
specialist · 615 · lc medium +29 · verified · 68.2% accepted · 1,578 likes · top 75%
Description
A wooden plank of length n has ants walking at 1 unit per second. Ants in array left move leftward; ants in right move rightward. When two ants collide they reverse directions, and any ant that reaches an end of the plank falls off immediately. Return the time when the last ant falls off.
Example 1:
Input: n = 4, left = [4,3], right = [0,1]
Output: 4
Explanation: In the image above:
-The ant at index 0 is named A and going to the right.
-The ant at index 1 is named B and going to the right.
-The ant at index 3 is named C and going to the left.
-The ant at index 4 is named D and going to the left.
The last moment when an ant was on the plank is t = 4 seconds. After that, it falls immediately out of the plank. (i.e., We can say that at t = 4.0000000001, there are no ants on the plank).
Example 2:
Input: n = 7, left = [], right = [0,1,2,3,4,5,6,7]
Output: 7
Explanation: All ants are going to the right, the ant at index 0 needs 7 seconds to fall.
Example 3:
Input: n = 7, left = [0,1,2,3,4,5,6,7], right = []
Output: 7
Explanation: All ants are going to the left, the ant at index 7 needs 7 seconds to fall.
Code
1
2
3