[question 5] Common Ancestor

src/main/java/com/algorithm/question5/FindSameAncestor.java

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+package com.algorithm.question5;
+
+public class FindSameAncestor {
+	public Node buildBinaryTree(int... datas) {
+		if(datas.length < 7) {
+			return null;
+		}
+
+		Node head = new Node(datas[0]);
+		head.left = new Node(datas[1]);
+		head.right = new Node(datas[2]);
+		head.left.left = new Node(datas[3]);
+		head.left.right = new Node(datas[4]);
+		head.right.left = new Node(datas[5]);
+		head.right.right = new Node(datas[6]);
+
+		return head;
+	}
+
+	public Node findSameAncestorInBinaryTree(Node head, Node node1, Node node2) {
+		if(head == null) {
+			return null;
+		}
+
+		boolean left = isNodeInTree(head.left, node1, node2);
+		boolean right = isNodeInTree(head.right, node1, node2);
+
+		if(left && right) {
+			return head;
+		} else if(left && !right) {
+			return findSameAncestorInBinaryTree(head.left, node1, node2);
+		} else if(!left && right) {
+			return findSameAncestorInBinaryTree(head.right, node1, node2);
+		}
+
+		return null;
+	}
+
+	private boolean isNodeInTree(Node head, Node node1, Node node2) {
+		if(head == null) {
+			return false;
+		}
+
+		if(head.data == node1.data || head.data == node2.data) {
+			return true;
+		}
+
+		return isNodeInTree(head.left, node1, node2) || isNodeInTree(head.right, node1, node2);
+	}
+
+	public Node findSameAncestorInSearchTree(Node head, Node node1, Node node2) {
+		if(head == null) {
+			return null;
+		}
+
+		int high = node1.data > node2.data ? node1.data : node2.data;
+		int low = node1.data == high ? node2.data : node1.data; 
+
+		if(head.data > low && head.data < high) {
+			return head;
+		} else if(head.data >= high){
+			return findSameAncestorInSearchTree(head.left, node1, node2);
+		} else if(head.data <= low) {
+			return findSameAncestorInSearchTree(head.right, node1, node2);
+		}
+
+		return null;
+	}
+}

src/main/java/com/algorithm/question5/Node.java

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+package com.algorithm.question5;
+
+public class Node {
+	public int data;
+	public Node left;
+	public Node right;
+
+	public Node(int data) {
+		this.data = data;
+	}
+}

src/test/java/com/algorithm/question5/mark/Test_findSameAncestor.java

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+package com.algorithm.question5.mark;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.algorithm.question5.FindSameAncestor;
+import com.algorithm.question5.Node;
+
+import static org.hamcrest.core.Is.is;
+
+public class Test_findSameAncestor {
+	private FindSameAncestor findSameAncestor = new FindSameAncestor();
+
+	@Test
+	public void findSameAncestorInBinaryTree_head_is_null() {
+		// setup
+		Node head = null;
+
+		// execute
+		Node result = findSameAncestor.findSameAncestorInBinaryTree(head, new Node(4), new Node(5));
+
+		// verify
+		Assert.assertEquals(null, result);
+	}
+
+	@Test
+	public void findSameAncestorInBinaryTree_only_head_is() {
+		// setup
+		Node head = new Node(1);
+
+		// execute
+		Node result = findSameAncestor.findSameAncestorInBinaryTree(head, new Node(4), new Node(5));
+
+		// verify
+		Assert.assertEquals(null, result);
+	}
+
+	@Test
+	public void findSameAncestorInBinaryTree_example() {
+		// setup
+		Node head = findSameAncestor.buildBinaryTree(1,2,3,4,5,6,7);
+
+		// execute
+		Node result1 = findSameAncestor.findSameAncestorInBinaryTree(head, new Node(4), new Node(5));
+		Node result2 = findSameAncestor.findSameAncestorInBinaryTree(head, new Node(4), new Node(6));
+
+		// verify
+		Assert.assertThat(result1.data, is(2));
+		Assert.assertThat(result2.data, is(1));
+	}
+
+	@Test
+	public void findSameAncestorInSearchTree_head_is_null() {
+		// setup
+		Node head = null;
+
+		// execute
+		Node result1 = findSameAncestor.findSameAncestorInSearchTree(head, new Node(4), new Node(5));
+
+		// verify
+		Assert.assertEquals(null, result1);
+	}
+
+	@Test
+	public void findSameAncestorInSearchTree_only_head_is() {
+		// setup
+		Node head = new Node(1);
+
+		// execute
+		Node result1 = findSameAncestor.findSameAncestorInSearchTree(head, new Node(4), new Node(5));
+
+		// verify
+		Assert.assertEquals(null, result1);
+	}
+
+	@Test
+	public void findSameAncestorInSearchTree_example() {
+		// setup
+		Node head = findSameAncestor.buildBinaryTree(4,2,6,1,3,5,7);
+
+		// execute
+		Node result1 = findSameAncestor.findSameAncestorInSearchTree(head, new Node(1), new Node(3));
+		Node result2 = findSameAncestor.findSameAncestorInSearchTree(head, new Node(1), new Node(7));
+
+		// verify
+		Assert.assertThat(result1.data, is(2));
+		Assert.assertThat(result2.data, is(4));
+	}
+
+}