Merge pull request #8025 from wugangca/BAEL-3349

BAEL-3349 Knapsack problem implementation in Java

algorithms-miscellaneous-5/src/main/java/com/baeldung/algorithms/knapsack/Knapsack.java

@@ -0,0 +1,36 @@
+package com.baeldung.algorithms.knapsack;
+
+public class Knapsack {
+
+    public int knapsackRec(int[] w, int[] v, int n, int W) {
+        if (n <= 0) {
+            return 0;
+        } else if (w[n - 1] > W) {
+            return knapsackRec(w, v, n - 1, W);
+        } else {
+            return Math.max(knapsackRec(w, v, n - 1, W), v[n - 1] + knapsackRec(w, v, n - 1, W - w[n - 1]));
+        }
+    }
+
+    public int knapsackDP(int[] w, int[] v, int n, int W) {
+        if (n <= 0 || W <= 0) {
+            return 0;
+        }
+
+        int[][] m = new int[n + 1][W + 1];
+        for (int j = 0; j <= W; j++) {
+            m[0][j] = 0;
+        }
+
+        for (int i = 1; i <= n; i++) {
+            for (int j = 1; j <= W; j++) {
+                if (w[i - 1] > j) {
+                    m[i][j] = m[i - 1][j];
+                } else {
+                    m[i][j] = Math.max(m[i - 1][j], m[i - 1][j - w[i - 1]] + v[i - 1]);
+                }
+            }
+        }
+        return m[n][W];
+    }
+}

algorithms-miscellaneous-5/src/test/java/com/baeldung/algorithms/knapsack/KnapsackUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.algorithms.knapsack;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class KnapsackUnitTest {
+
+    @Test
+    public void givenWeightsandValues_whenCalculateMax_thenOutputCorrectResult() {
+        final int[] w = new int[] { 23, 26, 20, 18, 32, 27, 29, 26, 30, 27 };
+        final int[] v = new int[] { 505, 352, 458, 220, 354, 414, 498, 545, 473, 543 };
+        final int n = 10;
+        final int W = 67;
+        final Knapsack knapsack = new Knapsack();
+
+        assertEquals(1270, knapsack.knapsackRec(w, v, n, W));
+        assertEquals(1270, knapsack.knapsackDP(w, v, n, W));
+    }
+
+    @Test
+    public void givenZeroItems_whenCalculateMax_thenOutputZero() {
+        final int[] w = new int[] {};
+        final int[] v = new int[] {};
+        final int n = 0;
+        final int W = 67;
+        final Knapsack knapsack = new Knapsack();
+
+        assertEquals(0, knapsack.knapsackRec(w, v, n, W));
+        assertEquals(0, knapsack.knapsackDP(w, v, n, W));
+    }
+
+    @Test
+    public void givenZeroWeightLimit_whenCalculateMax_thenOutputZero() {
+        final int[] w = new int[] { 23, 26, 20, 18, 32, 27, 29, 26, 30, 27 };
+        final int[] v = new int[] { 505, 352, 458, 220, 354, 414, 498, 545, 473, 543 };
+        final int n = 10;
+        final int W = 0;
+        final Knapsack knapsack = new Knapsack();
+
+        assertEquals(0, knapsack.knapsackRec(w, v, n, W));
+        assertEquals(0, knapsack.knapsackDP(w, v, n, W));
+    }
+}