blog/static/files/ib002/recursion/pyramid-slide-down/TopDown.java

import java.util.TreeMap;

public class TopDown {
    record Position(int row, int col) implements Comparable<Position> {
        public int compareTo(Position r) {
            if (row != r.row) {
                return Integer.valueOf(row).compareTo(r.row);
            }

            if (col != r.col) {
                return Integer.valueOf(col).compareTo(r.col);
            }

            return 0;
        }
    }

    public static int longestSlideDown(
            int[][] pyramid,
            TreeMap<Position, Integer> cache,
            Position position) {
        int row = position.row;
        int col = position.col;

        if (row >= pyramid.length || col < 0 || col >= pyramid[row].length) {
            return Integer.MIN_VALUE;
        }

        if (row == pyramid.length - 1) {
            return pyramid[position.row][position.col];
        }

        if (!cache.containsKey(position)) {
            int slideDown = Math.max(
                longestSlideDown(pyramid, cache, new Position(row + 1, col)),
                longestSlideDown(pyramid, cache, new Position(row + 1, col + 1)));
            cache.put(position, pyramid[row][col] + slideDown);
        }

        return cache.get(position);
    }

    public static int longestSlideDown(int[][] pyramid) {
        TreeMap<Position, Integer> cache = new TreeMap<>();
        return longestSlideDown(pyramid, cache, new Position(0, 0));
    }

    public static void main(String[] args) {
        System.out.print("Test #1: ");
        System.out.println(longestSlideDown(new int[][] {
                { 3 },
                { 7, 4 },
                { 2, 4, 6 },
                { 8, 5, 9, 3 }
        }) == 23 ? "passed" : "failed");

        System.out.print("Test #2: ");
        System.out.println(longestSlideDown(new int[][] {
                { 75 },
                { 95, 64 },
                { 17, 47, 82 },
                { 18, 35, 87, 10 },
                { 20, 4, 82, 47, 65 },
                { 19, 1, 23, 75, 3, 34 },
                { 88, 2, 77, 73, 7, 63, 67 },
                { 99, 65, 4, 28, 6, 16, 70, 92 },
                { 41, 41, 26, 56, 83, 40, 80, 70, 33 },
                { 41, 48, 72, 33, 47, 32, 37, 16, 94, 29 },
                { 53, 71, 44, 65, 25, 43, 91, 52, 97, 51, 14 },
                { 70, 11, 33, 28, 77, 73, 17, 78, 39, 68, 17, 57 },
                { 91, 71, 52, 38, 17, 14, 91, 43, 58, 50, 27, 29, 48 },
                { 63, 66, 4, 68, 89, 53, 67, 30, 73, 16, 69, 87, 40, 31 },
                { 4, 62, 98, 27, 23, 9, 70, 98, 73, 93, 38, 53, 60, 4, 23 },
        }) == 1074 ? "passed" : "failed");
    }
}