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 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.

题意：一个由0，1组成的数组，1代表栽了花，0代表空缺，栽花的规则是花不能相邻，求是否可以载n株花。

思路：

分类讨论。开头两个0就将第一个置1，最后两个0就将最后一个置1，中间连续出现三个0就将中间的置1，判断sum是否不小于n。注意数组只有一个元素的情况。

代码：

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