EqualStacks algorithm

Author: melmedany

src/main/java/EqualStacks.java

@@ -0,0 +1,104 @@
+/**
+ * @author medany
+ */
+
+public class EqualStacks {
+
+	public int solve(int[] s1, int[] s2, int[] s3) {
+
+		int result = 0;
+
+		s1 = reverse(s1);
+		s2 = reverse(s2);
+		s3 = reverse(s3);
+
+		s1 = sumAll(s1);
+		s2 = sumAll(s2);
+		s3 = sumAll(s3);
+
+		s1 = reverse(s1);
+		s2 = reverse(s2);
+		s3 = reverse(s3);
+
+		result = findFirstCommon(s1, s2, s3);
+
+		return result;
+	}
+
+	private int[] reverse(int[] arr) {
+		int[] reversed = new int[arr.length];
+		for (int i = 0; i < arr.length; i++) {
+			reversed[i] = arr[(arr.length - 1) - i];
+		}
+
+		return reversed;
+	}
+
+	// return a new array out of an existing array with each element is sum of all
+	// the previous elements
+	private int[] sumAll(int[] arr) {
+		int[] result = new int[arr.length];
+		int sum = 0;
+		for (int i = 0; i < arr.length; i++) {
+			sum += arr[i];
+			result[i] = sum;
+		}
+
+		return result;
+	}
+
+	private int findFirstCommon(int[] s1, int[] s2, int s3[]) {
+
+		if (s1.length < s2.length && s1.length < s3.length) {
+			for (int i = 0; i < s1.length; i++) {
+				for (int j = 0; j < s2.length; j++) {
+					if (s1[i] == s2[j]) {
+						for (int k = 0; k < s3.length; k++) {
+							if (s2[j] == s3[k]) {
+								return s1[i];
+							}
+						}
+					}
+				}
+			}
+		} else if (s2.length < s1.length && s2.length < s3.length) {
+			for (int i = 0; i < s2.length; i++) {
+				for (int j = 0; j < s1.length; j++) {
+					if (s2[i] == s1[j]) {
+						for (int k = 0; k < s3.length; k++) {
+							if (s1[j] == s3[k]) {
+								return s2[i];
+							}
+						}
+					}
+				}
+			}
+		} else if (s3.length < s1.length && s3.length < s2.length) {
+			for (int i = 0; i < s3.length; i++) {
+				for (int j = 0; j < s1.length; j++) {
+					if (s3[i] == s1[j]) {
+						for (int k = 0; k < s2.length; k++) {
+							if (s1[j] == s2[k]) {
+								return s3[i];
+							}
+						}
+					}
+				}
+			}
+		} else if (s1.length == s2.length && s2.length == s3.length) {
+			for (int i = 0; i < s1.length; i++) {
+				for (int j = 0; j < s2.length; j++) {
+					if (s1[i] == s2[j]) {
+						for (int k = 0; k < s3.length; k++) {
+							if (s2[j] == s3[k]) {
+								return s1[i];
+							}
+						}
+					}
+				}
+			}
+		}
+
+		return 0;
+	}
+}

test/main/java/EqualStacksTest.java

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+import org.junit.Assert;
+import org.junit.Test;
+
+/**
+ * @author medany
+ */
+
+public class EqualStacksTest {
+
+	private EqualStacks alg = new EqualStacks();
+	int actual, expected;
+
+	@Test
+	public void Test_1() {
+
+		actual = alg.solve(new int[] { 3, 2, 1, 1, 1 }, new int[] { 4, 3, 2 }, new int[] { 1, 1, 4, 1 });
+		expected = 5;
+
+		Assert.assertEquals(expected, actual);
+	}
+
+	@Test
+	public void Test_2() {
+
+		actual = alg.solve(new int[] { 1 }, new int[] { 1 }, new int[] { 1 });
+		expected = 1;
+
+		Assert.assertEquals(expected, actual);
+	}
+}