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);}}