Furthest Building You Can Reach

1public int furthestBuilding(int[] heights, int bricks, int ladders) {
2    // Min-heap of climbs where we used bricks
3    PriorityQueue<Integer> heap = new PriorityQueue<>();
4    int bricksUsed = 0;
5
6    for (int i = 0; i < heights.length - 1; i++) {
7        int climb = heights[i + 1] - heights[i];
8
9        if (climb <= 0) {
10            continue;  // no climb needed
11        }
12
13        // Use bricks for this climb
14        bricksUsed += climb;
15        heap.offer(climb);
16
17        if (bricksUsed > bricks) {
18            // Exceeded bricks, need a ladder
19            if (ladders == 0) {
20                return i;  // can't proceed
21            }
22
23            // Replace smallest climb with a ladder
24            int smallest = heap.poll();
25            bricksUsed -= smallest;
26            ladders--;
27        }
28    }
29
30    return heights.length - 1;
31}