main.cpp

#include <bits/stdc++.h>

using namespace std;

const int N = 3e5 + 5;

int n, k, p, prv[N];

int main() {
    // readining input
    scanf("%d %d", &n, &k);

    int last = -1, ans = 0;
    for (int i = 0; i < n; i++) {
        scanf("%d", &p);
        if(p == 1) last = i;
        prv[i] = last;
    }
    // end reading input

    for (int i = 0; i < n;) {
        int furthestPylon = prv[min(i + k - 1, n - 1)];
        if (furthestPylon == -1 || furthestPylon + k <= i) {
            printf("-1\n");
            return 0;
        }

        i = furthestPylon + k;
        ans++;
    }

    printf("%d\n", ans);

    return 0;

}

main.go

func pylons(k int32, cities []int32) int32 {
	var (
		coverRight, count = -1, int32(0)
	)

	for cityCur := 0; cityCur < len(cities); cityCur++ {
		if cities[cityCur] == 0 {
			continue
		}

		lastStable := cityCur
		potentialCityCur := cityCur
		score := 0
		newRight := coverRight
		for {
			if potentialCityCur >= len(cities) {
				cityCur = lastStable // <- possible optimization
				break
			}

			if cities[potentialCityCur] == 0 {
				potentialCityCur++
				continue
			}

			if left := potentialCityCur - int(k - 1); left > coverRight + 1 {
				cityCur = lastStable
				break 
			}

			lastStable = potentialCityCur
			newRight = lastStable + int(k - 1)
			score = 1
			potentialCityCur++
		}

		count += int32(score)
		coverRight = newRight
		if coverRight >= len(cities) - 1 {
			break
		}
	}

	if coverRight < len(cities) - 1 {
		return -1
	}

	return count
}