二叉树

二叉树的常见操作

import java.util.LinkedList;import java.util.Queue;import java.util.Stack;import javax.swing.LayoutStyle;import  java.util.ArrayList;class TreeNode {    int val;    TreeNode left;    TreeNode right;    TreeNode(int val){        this.val=val;        left=null;        right=null;    }}public class TreeSummary {    //递归中序    public static void inorder(TreeNode root){        if(root==null){            return;        }            inorder(root.left);            System.out.println(root.val);            inorder(root.right);    }    //递归前序    public static void preOrder(TreeNode root){          if(root!=null){              System.out.println(root.val);            preOrder(root.left);              preOrder(root.right);          }      }    //递归后序    public static void postOrder(TreeNode root){        if(root!=null){            postOrder(root.left);            postOrder(root.right);            System.out.println(root.val);        }    }    //非递归前序遍历    public static void norepreOrder(TreeNode root){        Stack<TreeNode>  stack=new Stack<TreeNode>();        TreeNode node=root;        while(node!=null||!stack.isEmpty()){            while(node!=null){                System.out.println(node.val);                stack.push(node);                node=node.left;            }            node=stack.pop();            node=node.right;        }    }    //非递归中序遍历    public static void noreinOrder(TreeNode root){        Stack<TreeNode>  stack=new Stack<TreeNode>();        TreeNode node=root;        while(node!=null||!stack.isEmpty()){            while(node!=null){                stack.push(node);                node=node.left;            }            if(!stack.isEmpty()){                node=stack.pop();                System.out.println(node.val);                node=node.right;            }        }    }    //非递归后序遍历    public static void norepostOrder(TreeNode root){        Stack<TreeNode> stack=new Stack<TreeNode>();        TreeNode node=root;        // 左子树入栈          for (; root.left != null; root = root.left)              stack.push(root.left);          while(root!=null&&(root.right==null||root.right==node)){            System.out.println(root);            node=root;            if (stack.empty())                  return;              root = stack.pop();         }        //处理右子树        stack.push(root);        root=root.right;    }    public static int getheight(TreeNode root){        if(root==null){            return 0;        }        else{            int i=getheight(root.left);            int j=getheight(root.right);            return (i<j)?(j+1):(i+1);        }    }    // 非递归后序遍历    public static void postorderTraversal(TreeNode root) {        Stack<TreeNode> treeNodeStack = new Stack<TreeNode>();        TreeNode node = root;        TreeNode lastVisit = root;        while (node != null || !treeNodeStack.isEmpty()) {            while (node != null) {                treeNodeStack.push(node);                node = node.left;            }            //查看当前栈顶元素            node = treeNodeStack.peek();            //如果其右子树也为空，或者右子树已经访问            //则可以直接输出当前节点的值            if (node.right == null || node.right == lastVisit) {                System.out.print(node.val + " ");                treeNodeStack.pop();                lastVisit = node;                node = null;            } else {                //否则，继续遍历右子树                node = node.right;            }        }    }    //层次遍历    public static void bfs(TreeNode root){        Queue<TreeNode>  queue=new LinkedList<TreeNode>();        TreeNode node=root;        while((node!=null)||(!queue.isEmpty())){            if(node!=null){                System.out.println(node.val);                queue.add(node.left);                queue.add(node.right);                node=queue.poll();            }            else{                node=queue.poll();            }        }    }    //搜索二叉树的第K个节点    TreeNode KthNode(TreeNode pRoot, int k)    {           if(k<=0 || pRoot==null )            return null;        ArrayList<TreeNode> list=new ArrayList<TreeNode>();        inorder(pRoot,list);        if(k>list.size())            return null;         return list.get(k-1);    }    public void inorder (TreeNode head,ArrayList<TreeNode> list){        if(head==null)            return;        inorder(head.left,list);        list.add(head);        inorder(head.right,list);    }    //判断是否是平衡二叉树    public boolean IsBalanced_Solution(TreeNode root){        if (root==null){            return true;        }        int leftheight=getHeight(root.left);        int rightheight=getHeight(root.right);        if(Math.abs(leftheight-rightheight)>1)            return false;        else{            return IsBalanced_Solution(root.left)&&IsBalanced_Solution(root.right);        }    }    public int getHeight(TreeNode root){        if(root==null)            return 0;        int leftHeight=getHeight(root.left);        int rightHeight=getHeight(root.right);        return rightHeight>leftHeight?rightHeight+1:leftHeight+1;    } }