二叉树笔试面试常见算法题

二叉树是笔试面试过程中常见的一种数据结构，而处理操作二叉树也是常见的算法题目，总结一下最近做的各种题目，记录一下自己之前写的相关基础算法，以后还会不断的增加自己遇到其他关于二叉树相关的算法题，为找工作做准备，感谢指正。

记录复习一下常用的二叉树相关的算法import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;public class outWay {public static void main(String[] args) {outWay ow = new outWay();int[] i = {4,8,9,6,1,3,2,7,0,5};TreeNode root = ow.buildTree(i);ow.findPath(root, 15);}//建立二叉树public TreeNode buildTree(int[] tree) {ArrayList<TreeNode> treelist = new ArrayList<TreeNode>();for(int i = 0; i<tree.length; i++) {treelist.add(new TreeNode(tree[i]));}for(int i = 0; i < treelist.size()/2 -1; i++) {treelist.get(i).left = treelist.get( 2*i + 1);treelist.get(i).right = treelist.get( 2*i + 2);}TreeNode lastParaentNode = treelist.get(treelist.size()/2 -1);lastParaentNode.left = treelist.get((treelist.size()/2 -1)*2 + 1);if(treelist.size()%2 == 1) {lastParaentNode.right = treelist.get((treelist.size()/2 -1)*2 + 2);}return treelist.get(0);}//前序遍历public void preTree(TreeNode root,ArrayList<Integer> pre) {if(root == null)return;pre.add(root.val);preTree(root.left, pre);preTree(root.right, pre);}//中序遍历public void inTree(TreeNode root,ArrayList<Integer> in) {if(root == null)return;inTree(root.left, in);in.add(root.val);inTree(root.right, in);}//后序遍历public void postTree(TreeNode root,ArrayList<Integer> post) {if(root == null)return;postTree(root.left, post);postTree(root.right, post);post.add(root.val);}//从上往下打印二叉树public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {ArrayList<Integer> list = new ArrayList<Integer>();if(root == null) return list;Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.offer(root);while(!queue.isEmpty()) {TreeNode currentNode = queue.poll();if(currentNode.left!=null) queue.offer(currentNode.left);if(currentNode.right!=null) queue.offer(currentNode.right);list.add(currentNode.val);}return list;}//根据前序遍历和中序遍历，重建二叉树public TreeNode reBuildTreeByPreIn(int[] pre,int[] in) { TreeNode root = usePreAndIn(pre,0,pre.length-1,in,0,in.length-1);     return root;}public TreeNode usePreAndIn(int[] pre,int preStart,int preEnd,int[] in,int inStart,int inEnd) {if(preStart > preEnd || inStart > inEnd) return null;TreeNode root = new TreeNode(pre[preStart]);for(int i=inStart; i<=inEnd; i++) {if(in[i] == pre[preStart]) {root.left = usePreAndIn(pre, preStart + 1, preStart + (i-inStart), in, inStart, i-1);root.right = usePreAndIn(pre, preStart+(i-inStart)+1, preEnd, in, i+1, inEnd);}}return root;}//判断B树是否为A树的子结构public boolean HasSubTree(TreeNode root1,TreeNode root2) {if(root1 ==null || root2 ==null) return false;return isSubTree(root1,root2) || HasSubTree(root1.left,root2) ||HasSubTree(root1.right,root2);}public boolean isSubTree(TreeNode root1,TreeNode root2) { if(root2 == null) return true;     if(root1 == null) return false;     if(root1.val == root2.val) {     return isSubTree(root1.left, root2.left) && isSubTree(root1.right, root2.right);     } else {     return false;     }}//打印出二叉树中结点值的和为输入整数的所有路径public ArrayList<ArrayList<Integer>> findPath(TreeNode root,int target) {ArrayList<ArrayList<Integer>> arraylist = new ArrayList<ArrayList<Integer>>();ArrayList<Integer> list = new ArrayList<Integer>();getPath(root, target, list, arraylist);return arraylist;}public void getPath(TreeNode root, int target, ArrayList<Integer> list, ArrayList<ArrayList<Integer>> arraylist) {if(root == null) return ;list.add(root.val);target -= root.val;if(target < 0) {list.remove(list.size() - 1);return ;}if(target == 0 && root.left ==null && root.right == null) {arraylist.add(new ArrayList<Integer>(list));}getPath(root.left,target,list,arraylist);getPath(root.right,target,list,arraylist);list.remove(list.size() - 1);}}