二叉树的遍历

一、求高度的函数

    public static <T extends Comparable<T>> int height(Node<T> root) {
        if(root == null) {
            return 0;
        }else {
            return height(root.getLeft())>height(root.getRight())?height(root.getLeft())+1:height(root.getRight())+1;
        }
    }

二、层次遍历二叉树

    public static <T extends Comparable<T>> void show(Node<T> root){
        int height = height(root);
        System.out.println(height);
        List<Node<T>> list = new ArrayList<Node<T>>();
        list.add(root);    
        for(int i=height;i>0;i--) {
            int len = list.size();
            int shu = (int)Math.pow(2, i-1);
            for(int j=0;j<len;j++) {
                for(int k=j*shu+(j-1>0?j-1:0)*shu;k<shu-1+j*shu*2;k++) {
                    System.out.printf("%-5s","");
                }
                Node<T> t =  list.get(0);
                if(t==null) {
                    System.out.printf("%-5s","x/x");
                    list.add(null);
                    list.add(null);
                }else {
                    System.out.printf("%-5s",t.getValue()+"/"+t.getHeight());
                    list.add(list.get(0).getLeft());
                    list.add(list.get(0).getRight());
                }
                list.remove(0);
            }
            System.out.println();
            System.out.println();
        }
    }

 二叉树的中序遍历

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result = new LinkedList<>();
        LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
        TreeNode tempNode = root;
        while (tempNode != null) {
            stack.push(tempNode);
            tempNode = tempNode.left;
        }
        while (!stack.isEmpty()) {
            tempNode = stack.pop();
            result.add(tempNode.val);
            tempNode = tempNode.right;
            while (tempNode != null) {
                stack.push(tempNode);
                tempNode = tempNode.left;
            }
        }
        return result;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }
}

 二叉树的前序遍历

class Solution {
    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> result = new LinkedList<>();
        LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
        TreeNode tempNode = root;
        while (tempNode != null) {
            stack.push(tempNode);
            result.add(tempNode.val);
            tempNode = tempNode.left;
        }
        while (!stack.isEmpty()) {
            tempNode = stack.pop();
            tempNode = tempNode.right;
            while (tempNode != null) {
                stack.push(tempNode);
                result.add(tempNode.val);
                tempNode = tempNode.left;
            }
        }
        return result;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }
}

 二叉树的后序遍历

class Solution {
    public List<Integer> postorderTraversal(TreeNode root) {
        List<Integer> result = new LinkedList<>();
        LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
        TreeNode tempNode = root;
        while (tempNode != null) {
            stack.push(tempNode);
            tempNode = tempNode.left;
        }
        while (!stack.isEmpty()) {
            tempNode = stack.peek();
            if (tempNode.right != null) {
                tempNode = tempNode.right;
                while (tempNode != null) {
                    stack.push(tempNode);
                    tempNode = tempNode.left;
                }
            } else {
                tempNode = stack.pop();
                result.add(tempNode.val);
                while (!stack.isEmpty() && stack.peek().right == tempNode) {
                    tempNode = stack.pop();
                    result.add(tempNode.val);
                }
            }
        }
        return result;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }
}