Example 2:
Input: root = [1,null,2]
Output: 2
Example 3:
Input: root = []
Output: 0
Example 4:
Input: root = [0]
Output: 1
Constraints:
-
The number of nodes in the tree is in the range [0, 10⁴].
-
-100 <= Node.val <= 10
方法一：递归版
方法二：非递归版（DFS）
方法三：方法三：非递归版(BFS)
public class MaximumDepthOfBinaryTree {
// 方法一：递归版(DFS)
public int maxDepth1(TreeNode root) {
if (root == null)
return 0;
return Math.max(maxDepth1(root.left), maxDepth1(root.right)) + 1;
}
// 方法二：非递归版(DFS)
public int maxDepth2(TreeNode root) {
if (root == null)
return 0;
int max = 1, count = 1;
LinkedList stack = new LinkedList<>(Arrays.asList(root, max));
TreeNode p = root;
while (true) {
if (p.left != null && p.right != null) {
count++;
stack.push(count);
stack.push(p.right);
p = p.left;
} else if (p.left != null && p.right == null) {
count++;
p = p.left;
} else if (p.left == null && p.right != null) {
count++;
p = p.right;
} else {
if (count > max)
max = count;
if (!stack.isEmpty()) {
p = (TreeNode) stack.pop();
count = (int) stack.pop();
} else {
break;
}
}
}
return max;
}
// 方法三：非递归版(BFS)
public int maxDepth3(TreeNode root) {
if (root == null)
return 0;
int count = 0;
TreeNode p = root;
LinkedList queue = new LinkedList(Arrays.asList(p));
while (!queue.isEmpty()) {
int size = queue.size();
while (size-- > 0) {
p = queue.poll();
if (p.left != null) {
queue.offer(p.left);
}
if (p.right != null) {
queue.offer(p.right);
}
}
count++;
}
return count;
}
}
import static org.junit.Assert.*;
import org.junit.Test;
import com.lun.util.BinaryTree.TreeNode;
public class MaximumDepthOfBinaryTreeTest {
@Test
public void test1() {
MaximumDepthOfBinaryTree obj = new MaximumDepthOfBinaryTree();
TreeNode root = new TreeNode(3);
root.left = new TreeNode(9);
root.right = new TreeNode(20);
root.right.left = new TreeNode(15);
root.right.right = new TreeNode(7);
assertEquals(3, obj.maxDepth1(root));
assertEquals(3, obj.maxDepth2(root));
assertEquals(3, obj.maxDepth3(root));
}
@Test
public void test2() {
MaximumDepthOfBinaryTree obj = new MaximumDepthOfBinaryTree();
TreeNode root = new TreeNode(1);
root.right = new TreeNode(2);
assertEquals(2, obj.maxDepth1(root));
assertEquals(2, obj.maxDepth2(root));
assertEquals(2, obj.maxDepth3(root));
}
@Test
public void test3() {
MaximumDepthOfBinaryTree obj = new MaximumDepthOfBinaryTree();
TreeNode root = null;
assertEquals(0, obj.maxDepth1(root));
assertEquals(0, obj.maxDepth2(root));
assertEquals(0, obj.maxDepth3(root));
}
