[LeetCode December Challange] Day 5 - Can Place Flowers

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:

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

---

Solution

Time complexity : O(n)
Space complexity : O(1)

class Solution {
public:
    bool canPlaceFlowers(vector<int>& flowerbed, int n) {
        int size = flowerbed.size();
        for (int i=0; i<size; ++i) {
            if ((0<i && flowerbed[i-1] == 1) ||
                (i<size-1 && flowerbed[i+1] == 1) ||
                flowerbed[i] == 1)
            {
                continue;
            }
            flowerbed[i] = 1;
            --n;
        }
        return n <= 0;
    }
};

從左至右，檢查下面幾點，若其一符合，則不種，跳過：

1. 左邊是否有種。
2. 右邊是否有種。
3. 自身是否有種。

其餘情況則種花，需求花數-1。
最後檢查種植數量是否大於需求花數(即需求為負)。