Skip to content

Latest commit

 

History

History
77 lines (62 loc) · 2.73 KB

README.md

File metadata and controls

77 lines (62 loc) · 2.73 KB

1964. Find the Longest Valid Obstacle Course at Each Position

You want to build some obstacle courses. You are given a 0-indexed integer array obstacles of length n, where obstacles[i] describes the height of the ith obstacle.

For every index i between 0 and n - 1 (inclusive), find the length of the longest obstacle course in obstacles such that:

  • You choose any number of obstacles between 0 and i inclusive.
  • You must include the ith obstacle in the course.
  • You must put the chosen obstacles in the same order as they appear in obstacles.
  • Every obstacle (except the first) is taller than or the same height as the obstacle immediately before it.

Return an array ans of length n, where ans[i] is the length of the longest obstacle course for index i as described above.

Example 1:

Input: obstacles = [1,2,3,2]
Output: [1,2,3,3]
Explanation: The longest valid obstacle course at each position is:
- i = 0: [1], [1] has length 1.
- i = 1: [1,2], [1,2] has length 2.
- i = 2: [1,2,3], [1,2,3] has length 3.
- i = 3: [1,2,3,2], [1,2,2] has length 3.

Example 2:

Input: obstacles = [2,2,1]
Output: [1,2,1]
Explanation: The longest valid obstacle course at each position is:
- i = 0: [2], [2] has length 1.
- i = 1: [2,2], [2,2] has length 2.
- i = 2: [2,2,1], [1] has length 1.

Example 3:

Input: obstacles = [3,1,5,6,4,2]
Output: [1,1,2,3,2,2]
Explanation: The longest valid obstacle course at each position is:
- i = 0: [3], [3] has length 1.
- i = 1: [3,1], [1] has length 1.
- i = 2: [3,1,5], [3,5] has length 2. [1,5] is also valid.
- i = 3: [3,1,5,6], [3,5,6] has length 3. [1,5,6] is also valid.
- i = 4: [3,1,5,6,4], [3,4] has length 2. [1,4] is also valid.
- i = 5: [3,1,5,6,4,2], [1,2] has length 2.

Constraints:

  • n == obstacles.length
  • 1 <= n <= 105
  • 1 <= obstacles[i] <= 107

Solutions (Python)

1. Solution

from sortedcontainers import SortedList


class Solution:
    def longestObstacleCourseAtEachPosition(self, obstacles: List[int]) -> List[int]:
        n = len(obstacles)
        sl = SortedList([(0, 0)])
        ans = [1] * n

        for i in range(n):
            j = sl.bisect_left((obstacles[i], n)) - 1
            ans[i] = sl[j][1] + 1

            if j + 1 < len(sl) and sl[j + 1][1] == ans[i]:
                sl.pop(j + 1)
            if sl[j][0] == obstacles[i]:
                sl.pop(j)

            sl.add((obstacles[i], ans[i]))

        return ans