二叉树面试总结 算法 java

二叉树面试中相关算法，java实现：

package com.js;

import java.util.LinkedList;
import java.util.Stack;

public class BinaryTree {
public class TreeRoot{
int data;
TreeRoot leftChild = null;
TreeRoot rightChild = null;
public TreeRoot(int data){
this.data = data;
}
}

/**
* 递归方式实现
* @param root
*/
private void preOrder(TreeRoot root){
if(root != null){
System.out.println(root.data);
preOrder(root.leftChild);
preOrder(root.rightChild);
}
}
private void inOrder(TreeRoot root){
if(root != null){
inOrder(root.leftChild);
System.out.println(root.data);
inOrder(root.rightChild);
}
}
private void postOrder(TreeRoot root){
if(root != null){
postOrder(root.leftChild);
postOrder(root.rightChild);
System.out.println(root.data);
}
}

/**
* 非递归方式实现
*/
private void noRecPreOrder(TreeRoot root){
Stack<TreeRoot> stack = new Stack();
while(root != null || stack.size() > 0){
while(root != null){
System.out.println(root.data);
stack.push(root);
root = root.leftChild;
}
if(stack.size() > 0){
root = stack.pop();
root = root.rightChild;
}
}
}

private void noRecInOrder(TreeRoot root){
Stack<TreeRoot> stack = new Stack();
while(root != null || stack.size() >0){
while(root != null){
stack.push(root);
root = root.leftChild;
}
if(stack.size() > 0){
root = stack.pop();
System.out.println(root.data);
root = root.rightChild;
}
}
}

private void onRecPostOrder(TreeRoot root){
Stack<TreeRoot> stack = new Stack();
TreeRoot node = root;
while(root != null){
//先左子树遍历
for(;root.leftChild != null;root = root.leftChild){
stack.push(root);
}
//当前节点无右子树 或者 右子树已经输出时
while(root != null && (root.rightChild == null || root.rightChild == node) ){
System.out.println(root.data);
node = root;
if(stack.empty()){
return;
}
root = stack.pop();
}
stack.push(root);
root = root.rightChild;
}
}

private void noRecPastOrder(TreeRoot root){
Stack<TreeRoot> stack = new Stack();
TreeRoot node = root;
while(root != null){
//遍历左子树 使他入栈
for(;root != null;root = root.leftChild){
stack.push(root);
}
//右子树是否等于空 或 右子树已经输出
while(root != null && (root.rightChild ==null || root.rightChild == node)){
System.out.println(root.data);
node = root;
if(stack.empty()){
return;
}
root = stack.pop();
}
stack.push(root);
root = root.rightChild;
}
}

/**
* 求叶子节点个数
* @param root
* @return
*/
private int getNodeNum(TreeRoot root){
if(root == null){
return 0;
}else{
return (getNodeNum(root.leftChild) +
getNodeNum(root.rightChild)) +1;
}
}

/**
* 求二叉树深度
*/
private int getDepth(TreeRoot root){
if(root == null){
return 0;
}else{
int leftDepth = getDepth(root.leftChild);
int rightDepth = getDepth(root.rightChild);
return (leftDepth > rightDepth ? leftDepth:rightDepth)+1;
}
}

/*
* 按层遍历二叉树
*/
private void levelTree(TreeRoot root){
LinkedList<TreeRoot> linkList = new LinkedList<>();
linkList.push(root);
while(!linkList.isEmpty()){
TreeRoot cur = linkList.removeFirst();
System.out.println(cur.data);
if(cur.leftChild != null){
linkList.add(cur.leftChild);
}
if(cur.rightChild != null){
linkList.add(cur.rightChild);
}
}
}

/*
* 求二叉树第K层节点个数
*/
private int getKNum(TreeRoot root ,int k){
if(root == null || k < 1){
return 0;
}
if(k == 1){
return 1;
}
int leftNum = getKNum(root,k-1);
int rightNum = getKNum(root, k-1);
return leftNum+rightNum;
}

/**
* 判断两个二叉树是否相同
*/
public boolean isSameRec(TreeRoot r1,TreeRoot r2){
if(r1 == null && r2 == null){
return true;
}else if(r1 == null || r2 == null){
return false;
}
if(r1.data == r2.data){
return true;
}
boolean leftSame = isSameRec(r1.leftChild,r2.leftChild);
boolean rightSame = isSameRec(r1.rightChild, r2.rightChild);
return leftSame && rightSame;
}

/**
* 检验二叉树是否是平衡二叉树
*/
public boolean isAVLRec(TreeRoot root){
if(root == null){
return true;
}
if(Math.abs(getDepth(root.leftChild) - getDepth(root.rightChild)) > 1){
return false;
}
return isAVLRec(root.leftChild) && isAVLRec(root.rightChild);
}
}