683

class Solution {
public:
    int kEmptySlots(vector<int>& bulbs, int k) {
        int n=bulbs.size();
        vector<int> days(n, INT_MAX);
        for(int i=0; i<n; i++)
            days[bulbs[i]-1] = i+1;

        int left = 0, right = left+k+1;
        int ans = INT_MAX;
        for(int i=0; right<n; i++){
            if(days[i] <  days[left] || days[i] <= days[right]){
                if(days[i] == days[right])
                    ans = min(ans, max(days[left], days[right]));
                left = i;
                right = left+k+1;
            }
        }
        return (ans == INT_MAX) ? -1 : ans;
    }
};