605. Can Place Flowers - Detailed Explanation

Problem Statement

Description:
You are given a flowerbed represented as an integer array flowerbed containing 0's and 1's, where 0 means an empty plot and 1 means a plot already has a flower planted. Flowers cannot be planted in adjacent plots. Given an integer n, determine if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule.

Example 1:

• Input:
  • flowerbed = [1, 0, 0, 0, 1]
  • n = 1
• Output: true
• Explanation:
  You can plant a flower in the middle plot (index 2) to get [1, 0, 1, 0, 1].

Example 2:

• Input:
  • flowerbed = [1, 0, 0, 0, 1]
  • n = 2
• Output: false
• Explanation:
  There is only one spot available to plant a new flower without violating the adjacent rule.

Example 3:

• Input:
  • flowerbed = [0, 0, 1, 0, 0]
  • n = 2
• Output: true
• Explanation:
  One valid planting is to place flowers at indices 0 and 3 (resulting in [1, 0, 1, 1, 0]), but note that careful checking of adjacent plots is required to ensure no two planted flowers become adjacent.

Constraints:

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

Hints

• Hint 1:
  You need to iterate through the array and, at each empty plot, check if its adjacent plots (or boundaries) are empty.

• Hint 2:
  Remember to treat the boundaries carefully: if the plot is at the start or end of the array, you only need to check one neighbor.

• Hint 3:
  When you plant a flower, mark that plot as planted (set it to 1) and skip the next plot since it cannot be used to plant another flower.

Approaches

Approach 1: Greedy Iteration

• Idea:
  Traverse the flowerbed and check for each plot if it is empty and its neighbors (if they exist) are also empty. If yes, plant a flower by setting that plot to 1 and decrement n. Continue until you finish scanning or n becomes 0.
• Details:
  • For index i, check if flowerbed[i] == 0.
  • For the left neighbor: if i == 0 or flowerbed[i-1] == 0.
  • For the right neighbor: if i == flowerbed.length - 1 or flowerbed[i+1] == 0.
  • If both conditions are true, plant a flower (flowerbed[i] = 1) and skip the next index.
• Benefits:
  This method is straightforward and runs in O(n) time with O(1) extra space.

Approach 2: Simulation with In-Place Updates

• Idea:
  Use a similar method to the greedy approach but simulate the planting process more explicitly. Update the array in-place and count the planted flowers.
• Benefits:
  This method is effectively the same as the greedy approach and uses constant extra space.

Code Implementations

Python Code