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.

Solution: use the greedy algorithm, plant flowers in each empty spot encountered from left to right without violating the rule.

 1 class Solution {
 2 public:
 3     bool canPlaceFlowers(vector<int>& flowerbed, int n) {
 4         flowerbed.insert(flowerbed.begin(),0);
 5         flowerbed.push_back(0);
 6         for(int i = 1; i < flowerbed.size()-1; ++i)
 7         {
 8             if(flowerbed[i-1] + flowerbed[i] + flowerbed[i+1] == 0)
 9             {
10                 --n;
11                 ++i;
12             }
13
14         }
15         return n <=0;
16     }
17 };