Problem description:

You have a long flowerbed in which some of the plots are planted, and some are not. However, flowers cannot be planted in adjacent plots.

Given an integer array flowerbed containing 0‘s and 1‘s, where 0 means empty and 1 means not empty, and an integer n, return if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule.

Example 1:

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Input: flowerbed = [1,0,0,0,1], n = 1
Output: true

Example 2:

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Input: flowerbed = [1,0,0,0,1], n = 2
Output: false

Constraints:

  • 1 <= flowerbed.length <= 2 * 104
  • flowerbed[i] is 0 or 1.
  • There are no two adjacent flowers in flowerbed.
  • 0 <= n <= flowerbed.length

Solution:

We could walk through the array, if we find this spot flowerbed[i] could plant flower, then n -= 1

How do we know if a spot flowerbed[i] could plant?

  1. the value should be 0
  2. previous spot flowerbed[i-1] is 0 or we’re at first spot flowerbed[0] and next spot is 0
  3. next spot flowerbed[i+1] is 0 or we’re at last spot flowerbed[-1] and previous spot is 0
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class Solution:
    def canPlaceFlowers(self, flowerbed: List[int], n: int) -> bool:
        for i, x in enumerate(flowerbed):
            if not x and (i == 0 or flowerbed[i-1] == 0) and (i == len(flowerbed)-1 or flowerbed[i+1] == 0):
                n -= 1
                flowerbed[i] = 1
        return n <= 0

time complexity: $O(n))$
space complexity: $O(1)$
reference:
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