683. K Empty Slots

here is a garden with N slots. In each slot, there is a flower. The N flowers will bloom one by one in N days. In each day, there will be exactly one flower blooming and it will be in the status of blooming since then.

Given an array flowers consists of number from 1 to N. Each number in the array represents the place where the flower will open in that day.

For example, flowers[i] = x means that the unique flower that blooms at day i will be at position x, where i and x will be in the range from 1 to N.

Also given an integer k, you need to output in which day there exists two flowers in the status of blooming, and also the number of flowers between them is k and these flowers are not blooming.

If there isn't such day, output -1.

Example 1:

Input: 
flowers: [1,3,2]
k: 1
Output: 2
Explanation: In the second day, the first and the third flower have become blooming.

 

Example 2:

Input: 
flowers: [1,2,3]
k: 1
Output: -1

 

Note:

class Solution {
public:
    int kEmptySlots(vector<int>& flowers, int k) {
        set<int> bloom;
        for (int i = 0; i < flowers.size(); i++) {
            int p = flowers[i];
            auto it = bloom.insert(p).first;
            if (it != bloom.begin()) {
                if (p-*(--it) == k+1) return i+1;
                it++;
            }
            if (++it != bloom.end() && *it-p == k+1) return i+1; 
        }
        return -1;
    }
};