From 993716627a616e821aefd8707230221d0dac6cd7 Mon Sep 17 00:00:00 2001
From: Haidong Ji
Date: Thu, 27 Dec 2018 09:48:28 -0600
Subject: Knapsack partition3 done!

I used the "sleep on it" technique and the algo came to me about the
time I fall asleep. I started working on this based on algo I thought in
my head first thing after my run and shower, and it worked! I then went
to edX forum to see what other people are saying. Frankly those forum
posts were confusing to me.---
 .../sources/Partition3.java                        | 63 ++++++++++++++++++++++
 .../tests/Partition3Test.java                      | 25 +++++++++
 2 files changed, 88 insertions(+)
 create mode 100644 AlgoDesignAndTechniqueEdxJava/sources/Partition3.java
 create mode 100644 AlgoDesignAndTechniqueEdxJava/tests/Partition3Test.java

diff --git a/AlgoDesignAndTechniqueEdxJava/sources/Partition3.java b/AlgoDesignAndTechniqueEdxJava/sources/Partition3.java
new file mode 100644
index 0000000..546fcb2
--- /dev/null
+++ b/AlgoDesignAndTechniqueEdxJava/sources/Partition3.java
@@ -0,0 +1,63 @@
+import java.util.Scanner;
+
+public class Partition3 {
+
+    public static void main(String[] args) {
+        Scanner scanner = new Scanner(System.in);
+        int n = scanner.nextInt();
+        int[] A = new int[n];
+        for (int i = 0; i < n; i++) {
+            A[i] = scanner.nextInt();
+        }
+        System.out.println(partition3(A));
+    }
+
+    public static int partition3(int[] a) {
+        if (a.length < 3)
+            return 0;
+        int sum = 0;
+        for (int i = 0; i < a.length; i++) {
+            sum = sum + a[i];
+        }
+        if (sum % 3 != 0)
+            return 0;
+        int W = sum / 3;
+        int[][] values = optimalWeight2DArray(W, a);
+        int count = 0;
+        for (int i = 1; i < a.length + 1; i++) {
+            for (int w = 1; w < W + 1; w++) {
+                if (values[w][i] == W)
+                    count = count + 1;
+            }
+        }
+        if (count >= 3)
+            return 1;
+        else
+            return 0;
+    }
+
+    public static int[][] optimalWeight2DArray(int W, int[] w2) {
+        int j = w2.length;
+        int[][] value = new int[W + 1][j + 1];
+
+        for (int i = 0; i < j + 1; i++) {
+            for (int w = 0; w < W + 1; w++) {
+                if (i == 0 || w == 0) {
+                    value[w][i] = 0;
+                    continue;
+                }
+                value[w][i] = value[w][i - 1];
+                if (w2[i - 1] <= w) {
+                    int val = value[w - w2[i - 1]][i - 1] + w2[i - 1];
+                    if (value[w][i] < val) {
+                        value[w][i] = val;
+                    }
+                }
+            }
+
+        }
+
+        return value;
+    }
+
+}
diff --git a/AlgoDesignAndTechniqueEdxJava/tests/Partition3Test.java b/AlgoDesignAndTechniqueEdxJava/tests/Partition3Test.java
new file mode 100644
index 0000000..593d21a
--- /dev/null
+++ b/AlgoDesignAndTechniqueEdxJava/tests/Partition3Test.java
@@ -0,0 +1,25 @@
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class Partition3Test {
+
+    @Test
+    void test() {
+        int[] a = {3, 3, 3, 3};
+        assertEquals(0, Partition3.partition3(a));
+    }
+
+    @Test
+    void test1() {
+        int[] a = {30};
+        assertEquals(0, Partition3.partition3(a));
+    }
+
+    @Test
+    void test2() {
+        int[] a = {1, 2, 3, 4, 5, 5, 7, 7, 8, 10, 12, 19, 25};
+        assertEquals(1, Partition3.partition3(a));
+    }
+
+}
-- 
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