Can Place Flowers

Suppose 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 - they would compete for water and both would die.

Given a flowerbed (represented as an array containing 0 and 1, where 0 means empty and 1 means not empty), and a numbern, return ifnnew flowers can be planted in it without violating the no-adjacent-flowers rule.

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

Note:

1. The input array won't violate no-adjacent-flowers rule.

2. The input array size is in the range of [1, 20000].

3. n is a non-negative integer which won't exceed the input array size.

Solution

One pass - linear scan - greedy

O(n) time, O(1) space

class Solution {
    public boolean canPlaceFlowers(int[] flowerbed, int n) {
        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--;
            }

            if (n <= 0) {
                return true;
            }
        }
        return false;
    }
}