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package byteDance;
import java.util.LinkedList;
import java.util.Queue;
/**
* Created by lizeyang on 2020/5/14.
* 二叉树最大深度，最小深度
*/
public class test21 {
/*
* 二叉树深度：
* 1.二叉树只有一个节点，深度为1
* 2.二叉树的左子树为空，深度为右子树深度+1；
* 3.二叉树的右子树为空，深度为左子树深度+1；
* 4.二叉树的左子树，右子树都不为空，最大深度为左右子树深度最大值+1，最小深度为左右子树最小值+1。
* */
//最大深度递归实现
public static int maxDepth(TreeNode root) {
if (root == null) {
return 0;
}
if(root.left==null){
return maxDepth(root.right)+1;
}
if(root.right==null){
return maxDepth(root.left)+1;
}
int left = maxDepth(root.left);
int right = maxDepth(root.right);
return Math.max(left, right) + 1;
}
//最大深度非递归实现——层次遍历
public static int maxDepthNonRecur(TreeNode root) {
if (root == null) {
return 0;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int level = 0;
while (!queue.isEmpty()) {
int size = queue.size();
level++;
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
}
return level;
}
//最小深度递归实现
public static int minDepth(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null) {
return minDepth(root.right) + 1;
}
if (root.right == null) {
return minDepth(root.left) + 1;
}
return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
}
//最小深度非递归实现-层次遍历
public static int minDepthNonRecu(TreeNode root) {
if (root == null) {
return 0;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int level = 0;
while (!queue.isEmpty()) {
int size = queue.size();
level++;
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
//一旦遇到叶子节点，即最短深度
if (node.left == null && node.right == null) {
return level;
}
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
}
return level;
}
public static void main(String[] args) {
TreeNode root = new TreeNode(5);
root.left = new TreeNode(4);
root.right = new TreeNode(8);
root.left.left = new TreeNode(3);
root.right.left = new TreeNode(7);
root.right.left.left = new TreeNode(6);
root.right.right = new TreeNode(9);
System.out.println(maxDepth(root));
System.out.println(maxDepthNonRecur(root));
System.out.println(minDepth(root));
System.out.println(minDepthNonRecu(root));
}
}