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0605 - Can Place Flowers (Easy)

https://leetcode.com/problems/can-place-flowers/

Problem Statement​

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 true if n new flowers can be planted in the flowerbed without violating the no-adjacent-flowers rule and false otherwise.

Example 1:

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

Example 2:

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

Constraints:

  • 1 <= flowerbed.length <= 2 * 10^4
  • flowerbed[i] is 0 or 1.
  • There are no two adjacent flowers in flowerbed.
  • 0 <= n <= flowerbed.length

Approach 1: STL​

Simplest approach to check is to iterate over the elements and check the prev[i - 1] and next[i + 1] elements to statisfy the constraint.

If given n is 0 return true, or if n is higher than the no. of plots available to plant in an array adjacently then return false.

Time Complexity: O(n)O(n), where nn - # of elements in the array

Space Complexity: O(1)O(1)

Written by @vigneshshiv
class Solution {
    public boolean canPlaceFlowers(int[] flowerbed, int n) {
        // Case 1. No flowers to plant, so return true
        if (n == 0) return true;
        // Case 2. If No. of flowers to plant adajacently is higher than the half flowerbed array 
        int range = (flowerbed.length / 2) + ((flowerbed.length & 1) == 0 ? 0 : 1);
        if (n > range) return false;
        // Case 3. Iterate to check prev[i - 1] and next[i + 1] elements to satisfy the constraint
        for (int i = 0; i < flowerbed.length; i++) {
            if (flowerbed[i] == 0 && (i == 0 || flowerbed[i - 1] == 0) && (i == flowerbed.length - 1 || flowerbed[i + 1] == 0)) {
                flowerbed[i] = 1;
                n -= 1;
                if (n == 0) return true;
            }
        }
        return false;
    }
}