Box Stacking

Author: giaunv

datastructure-algorithm-java-examples/src/main/java/com/hellokoding/algorithm/DP_BoxStacking.java

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+package com.hellokoding.algorithm;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+public class DP_BoxStacking {
+    static class Box {
+        int height;
+        int width;
+        int depth;
+        int area;
+
+        Box(int height, int width, int depth) {
+            this.height = height;
+            this.width = width;
+            this.depth = depth;
+            this.area = this.width * this.depth;
+        }
+    }
+
+    static int findMaxHeight(Box[] arr, int N) {
+        Box[] boxes = new Box[N*3];
+
+        for (int i = 0; i < N; i++) {
+            Box current = arr[i];
+            boxes[i*3] = new Box(current.height, Math.max(current.width, current.depth), Math.min(current.width, current.depth));
+            boxes[i*3 + 1] = new Box(current.width, Math.max(current.height, current.depth), Math.min(current.height, current.depth));
+            boxes[i*3 + 2] = new Box(current.depth, Math.max(current.height, current.width), Math.min(current.height, current.width));
+        }
+
+        Arrays.sort(boxes, Comparator.comparing(x -> x.area, Comparator.reverseOrder()));
+        N *= 3;
+
+        int[] maxHeights = new int[N];
+        for (int i = 0; i < N; i++) {
+            maxHeights[i] = boxes[i].height;
+        }
+
+        for (int i = 0; i < N; i++) {
+            int maxHeightBeforeI = 0;
+            for (int j = 0; j < i; j++) {
+                if (boxes[j].width > boxes[i].width && boxes[j].depth > boxes[i].depth)
+                    maxHeightBeforeI =  Math.max(maxHeightBeforeI, maxHeights[j]);
+            }
+            maxHeights[i] = maxHeightBeforeI + boxes[i].height;
+        }
+
+        return Arrays.stream(maxHeights).max().getAsInt();
+    }
+
+    public static void main(String[] args) {
+        Box[] arr = new Box[4];
+        arr[0] = new Box(4, 6, 7);
+        arr[1] = new Box(1, 2, 3);
+        arr[2] = new Box(4, 5, 6);
+        arr[3] = new Box(10, 12, 32);
+
+        System.out.println(findMaxHeight(arr, 4));
+    }
+}