778-Swim-in-Rising-Water.java

// Solution: Greedy Approach with Min Heap
// Time Complexity: O((n^2)*log(n))
class Solution {

    private int[][] dirs = { { -1, 0 }, { 1, 0 }, { 0, -1 }, { 0, 1 } };

    public int swimInWater(int[][] grid) {
        int len = grid.length;

        if (len == 1) {
            return 0;
        }

        var seen = new boolean[len][len];
        seen[0][0] = true;

        var minHeap = new PriorityQueue<Integer[]>((a, b) -> a[0] - b[0]);
        minHeap.add(new Integer[] { grid[0][0], 0, 0 });

        int result = 0;

        while (!minHeap.isEmpty()) {
            var curr = minHeap.poll();

            result = Math.max(result, curr[0]);

            if (curr[1] == len - 1 && curr[2] == len - 1) {
                break;
            }

            for (int i = 0; i < 4; i++) {
                int x = curr[1] + dirs[i][0];
                int y = curr[2] + dirs[i][1];

                if (x < 0 || x >= len || y < 0 || y >= len || seen[x][y]) {
                    continue;
                }

                minHeap.add(new Integer[] { grid[x][y], x, y });
                seen[x][y] = true;
            }
        }

        return result;
    }
}