605. 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.

S: greedy O(n)

只要当前和前后位置为0就种上花, 并把当前位置置1， 直到n == 0

    bool canPlaceFlowers(vector<int>& flowerbed, int n) {
        int size = flowerbed.size();
        if (size < n) return false;
        if (n == 0) return true;  //注意n == 0的cornercase
        for (int i = 0; i < size; ++i) {
            if (flowerbed[i] == 0 && (i == 0 || flowerbed[i - 1] == 0) &&
                (i == size - 1 || flowerbed[i + 1] == 0)) {
                    n--;
                    flowerbed[i] = 1;
                    if (n == 0) return true;
                }
        }
        return false;
    }