LeetCode 605. Can Place Flowers

原题链接在这里：https://leetcode.com/problems/can-place-flowers/

题目：

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 number n, return if n new 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.

题解：

当前值为0时看前一个和后一个是否同时为0, 若是就可以栽花. 注意首尾特殊情况.

Time Complexity: O(flowerbed.length).

Space: O(1).

AC Java:

class Solution {
    public boolean canPlaceFlowers(int[] flowerbed, int n) {
        if(flowerbed == null){
            throw new IllegalArgumentException("Input array is null.");
        }
        
        int count = 0;
        for(int i = 0; i<flowerbed.length && count<n; i++){
            if(flowerbed[i] == 0){
                int pre = (i == 0) ? 0 : flowerbed[i-1];
                int next = (i == flowerbed.length-1) ? 0 : flowerbed[i+1];
                if(pre == 0 && next == 0){
                    count++;
                    flowerbed[i] = 1;
                }
            }
        }
        return count == n;
    }
}