二叉树算法题

package demo;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;


public class BalanceTree {
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x) { val = x; }
    }

    /**
     * 平衡二叉树
     * @param root
     * @return
     */
    public boolean isBalanced(TreeNode root) {
        return depth(root) != -1;
    }

    private int depth(TreeNode root) {
        if (root == null){
            return 0;
        }
        int left = depth(root.left);
        if(left == -1) {
            return -1;
        }
        int right = depth(root.right);
        if(right == -1) {
            return -1;
        }
        return Math.abs(left - right) < 2 ? Math.max(left, right) + 1 : -1;
    }


    /**
     * 二叉树最大深度
     * @param root
     * @return
     */
    public int maxDepth(TreeNode root) {

        if (null == root){
            return 0;
        }

        int leftDepth = maxDepth(root.left);
        int rightDepth = maxDepth(root.right);
        return Math.max(leftDepth,rightDepth)+1;
    }


    //二叉树最小深度
    public int minDepth(TreeNode root) {
        if (null == root){
            return 0;
        }
        int leftDepth = minDepth(root.left);
        int rightDepth = minDepth(root.right);

        if (0 != leftDepth && 0 != rightDepth){
            return Math.min(leftDepth,rightDepth)+1;
        }
        return Math.max(leftDepth,rightDepth)+1;

    }

    /**
     * 层次变量二叉树
     * @param root
     * @return
     */
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> resultList=new LinkedList<>();
        if (null == root){
            return resultList;
        }
        LinkedList<TreeNode> nodeQueue = new LinkedList<>();
        nodeQueue.add(root);
        while (!nodeQueue.isEmpty()){
            int currentLevel = nodeQueue.size();
            List<Integer> currentNodeList = new LinkedList<>();
            while (currentLevel>0){
                currentLevel--;
                TreeNode currentNode = nodeQueue.poll();
                if (null == currentNode){
                    continue;
                }
                currentNodeList.add(currentNode.val);
                if (null != currentNode.left){
                    nodeQueue.add(currentNode.left);
                }
                if (null != currentNode.right){
                    nodeQueue.add(currentNode.right);
                }

            }
            resultList.add(currentNodeList);
        }

        return resultList;
    }


    /**
     * 递归求二叉树左视图
     * @param root
     * @return
     */
    public void treeLeftView(TreeNode root,List<Integer> leftViewNodeList,int currentLevel) {
        //List<Integer> leftViewNodeList=new LinkedList<>();
        if (null == root){
            return ;
        }
        if (currentLevel == leftViewNodeList.size()){
            leftViewNodeList.add(root.val);
        }

        treeLeftView(root.left,leftViewNodeList,currentLevel++);
        treeLeftView(root.right,leftViewNodeList,currentLevel++);
    }
    /**
     * 递归求二叉树右视图
     * @param root
     * @return
     */
    public void treeRightView(TreeNode root,List<Integer> leftViewNodeList,int currentLevel) {
        //List<Integer> leftViewNodeList=new LinkedList<>();
        if (null == root){
            return ;
        }
        if (currentLevel == leftViewNodeList.size()){
            leftViewNodeList.add(root.val);
        }
        treeLeftView(root.right,leftViewNodeList,currentLevel++);
        treeLeftView(root.left,leftViewNodeList,currentLevel++);
    }

    /**
     * 求视图并打印
     * @param root
     */
    public void leftView(TreeNode root){
        if (null  == root){
            return;
        }
        List<Integer> leftViewNodeList = new LinkedList<>();
        int currentLevel = 0;
        treeLeftView(root,leftViewNodeList,currentLevel);
        //打印
        leftViewNodeList.forEach((node)-> System.out.println(node));
    }

}