605. 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.

Greedy Solution-I

• The code is self explanatory.
• Time Complexity: O(N)
• Space Complexity: O(1)

Code

class Solution {
public:
    bool canPlaceFlowers(vector<int>& flowerbed, int n)
    {
        int m = flowerbed.size();
        if (m == 1 && flowerbed[0] == 0) // if only one flowerbed and it is empty
            return n <= 1;

        for (int i = 0; i < m; i++) {
            if (i == 0) { // first element
                if (flowerbed[i] == 0 && flowerbed[i + 1] == 0) {
                    flowerbed[i] = 1;
                    --n;
                }
            } else if (i == m - 1) { // last element
                if (flowerbed[i - 1] == 0 && flowerbed[i] == 0) {
                    flowerbed[i] = 1;
                    --n;
                }
            } else { // other elements
                if (flowerbed[i - 1] == 0 && flowerbed[i] == 0 && flowerbed[i + 1] == 0) {
                    flowerbed[i] = 1;
                    --n;
                }
            }
        }

        return n <= 0;
    }
};

Greedy Solution-II

• Solution by using pre for previous element and next for next element.
• Time Complexity: O(N)
• Space Complexity: O(1)

Code

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