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

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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");
}
}