java实现树

面试题25：二叉树中和为某一值的路径

题目：输入一颗二叉树和一个整数，打印出二叉树中结点值的和为输入整数的所有路径。
从树的根结点开始往下一直到叶结点所经过的结点形成一条路径。二叉树节点的定义如下：
class BinaryTreeNode{
    String data;
    BinaryTreeNode left;
    BinaryTreeNode right;

}  

注：Stack为java实现栈中的Stack

public class FindPath_25 {public static void main(String []args) {BinaryTreeNode node1 = new BinaryTreeNode(10);BinaryTreeNode node2 = new BinaryTreeNode(5);BinaryTreeNode node3 = new BinaryTreeNode(12);BinaryTreeNode node4 = new BinaryTreeNode(4);BinaryTreeNode node5 = new BinaryTreeNode(7);node1.connection(node1, node2, node3);node1.connection(node2, node4, node5);findPath(node1,22);}private static void findPath(BinaryTreeNode root, int expectValue) {if(root==null) return;Stack<Integer> stack = new Stack<Integer>();int currentSum = 0;findPath(root,expectValue,stack,currentSum);//System.out.println(stack.empty());}private static void findPath(BinaryTreeNode root, int expectValue,Stack<Integer> stack, int currentSum) {currentSum += root.data;stack.push(root.data);//如果是叶子结点，并且路径上结点的和等于输入的值，打印出这条路径    boolean leaf = root.left == null && root.right == null;    if(currentSum==expectValue&&leaf) {    for(int i=stack.storage.size()-1;i>=0;i--) {    System.out.print(stack.storage.get(i)+" ");    }    System.out.println();    }        //如果不是叶子结点，则遍历它的子节点    if(root.left!=null) findPath(root.left,expectValue,stack,currentSum);    if(root.right!=null) findPath(root.right,expectValue,stack,currentSum);        stack.pop();}}class BinaryTreeNode{    int data;    BinaryTreeNode left;    BinaryTreeNode right;        BinaryTreeNode(int data) {    this.data = data;    left = null;    right = null;    }        public void connection(BinaryTreeNode root,BinaryTreeNode left,BinaryTreeNode right) {    if(root == null) return;    root.left = left;    root.right = right;    }} 

面试题24：二叉搜索树的后序遍历序列

题目：输入一个整数数组，判断该数组是不是某二叉搜索树的后序遍历结果。
如果是则返回true，否则返回false。假设输入数组的任意两个数字都互不相同。

public class SquenceOfBST {public static void main(String []args) {int[] squence = {5,7,6,9,11,10,8};System.out.println(VerifySquenceOfBST(squence,squence.length));}private static boolean VerifySquenceOfBST(int[] squence, int length) {if(squence==null||length<=0) return false;int root = squence[length-1];//在二叉树中左子树的节点小于根节点int i=0;for(;i<length-1;i++) {if(root<squence[i]) {break;}}//在二叉树中右子树的节点大于根节点int j = i;for(;j<length-1;j++) {if(root>squence[j]) {return false;} }//求出左右子树int squenceLeft[] = new int[i];int squenceRight[] = new int[j-i];for(int z=0;z<i;z++) {squenceLeft[z] = squence[z];}for(int z=0;z<j-i;z++) {squenceRight[z] = squence[i+z];}//判断左子树是不是二叉搜索树boolean left = true;if(i>0) left = VerifySquenceOfBST(squenceLeft,squenceLeft.length);//判断右子树是不是二叉搜索树boolean right = true;if(j-i>0) right = VerifySquenceOfBST(squenceRight,squenceRight.length);return left&&right;}}

面试题23：从上往下打印二叉树

题目：从上往下打印出二叉树的每个结点，同一层的结点按照从左到右的顺序打印。

类BitreeMirrorImg在下面的二叉树的镜像中。

import java.util.LinkedList;public class PrintFromTopToBottom_23 {public static void main(String[] args) {BitreeMirrorImg bm  = new BitreeMirrorImg();BinaryTreeNode root = null;root = bm.createTree(root);System.out.println(root);printFromToBottom(root);}public static void printFromToBottom(BinaryTreeNode root) {if(root==null) {return;}LinkedList<BinaryTreeNode> queue  = new LinkedList<BinaryTreeNode>();queue.add(root);while(queue.size()>0) {BinaryTreeNode bt = queue.poll();System.out.print(bt.data + " ");if(bt.left!=null) queue.add(bt.left);if(bt.right!=null) queue.add(bt.right);}} }

面试题19：二叉树的镜像

题目：请完成一个函数，输入一个二叉树，该函数输出它的镜像

import java.util.Scanner;//二叉树的结构class BinaryTreeNode{    String data;    BinaryTreeNode left;    BinaryTreeNode right;}/** *  输入一个二叉树，输出它的镜像 */public class BitreeMirrorImg {    Scanner scanner = new Scanner(System.in);    //建立二叉树    public BinaryTreeNode createTree(BinaryTreeNode root){        String data;        data = scanner.next();        if(data.equals("#")){            return null;        }        root = new BinaryTreeNode();        root.data = data;        root.left = createTree(root.left);        root.right = createTree(root.right);        return root;    }    //得到二叉树的镜像    public void mirror(BinaryTreeNode root){        if(root == null){            return;        }        if((root.left == null) && (root.right == null)){            return;        }        BinaryTreeNode temp = root.left;        root.left = root.right;        root.right = temp;        mirror(root.left);        mirror(root.right);    }    //层次遍历二叉树    public void levelTraverse(BinaryTreeNode root){        java.util.LinkedList<BinaryTreeNode> list= new java.util.LinkedList<BinaryTreeNode>();        list.add(root);        while(list.size() != 0){            BinaryTreeNode node = list.removeFirst();            System.out.print(node.data + " ");            if(node.left != null){                list.add(node.left);            }            if(node.right != null){                list.add(node.right);            }        }    }    public static void main(String[] args) {        BitreeMirrorImg bmi = new BitreeMirrorImg();        BinaryTreeNode root = null;        root = bmi.createTree(root);        bmi.mirror(root);        bmi.levelTraverse(root);    }}