版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/maguochao_Mark/article/details/51265302

【数据结构与算法】十五 二叉树遍历 DFS 深度优先 递归算法

结合上一篇的二叉树文章.
遍历即将树的所有结点访问且仅访问一次.
Depth-First-Search 深度优先
基于深度优先算法有三种

前序遍历：根节点->左子树->右子树

private void preorder(Node node){
if(null == node)
return ;
System.out.print(node.value);
preorder(node.left);
preorder(node.right);
}

中序遍历：左子树->根节点->右子树

private void midorder(Node node){
if(null == node)
return ;
midorder(node.left);
System.out.print(node.value);
midorder(node.right);
}

后序遍历：左子树->右子树->根节点

private void postorder(Node node){
if(null == node)
return ;
postorder(node.left);
postorder(node.right);
System.out.print(node.value);
}

完整code

package com.cn.mark.algorithm.binarytree;

public class BST <T extends Comparable<? super T>>{

private static class Node<T> {

private T value ;
private Integer position ;
private Integer height ;
private Node<T> left;
private Node<T> right;

public Node(T value , Integer position, Node<T> left, Node<T> right) {
this.value =  value;
this.position = position ;
this.height = 0;
this.left = left;
this.right = right;
}
}

private int height(Node<T> t) {
return t == null ? -1 : t.height;
}

private Node<T> root ;

public void add(T value , Integer position){
root = add( value , position, root );
}

private Node<T> add(T value , Integer position, Node<T> node){
if(node == null){
return new Node<T>(value,position , null ,null);
}

int comparaResult = value.compareTo(node.value);

if(comparaResult > 0)
node.right = add(value , position , node.right);
else if (comparaResult < 0)
node.left = add(value , position , node.left);
else
System.out.println("as same a value");

node.height = Math.max(height(node.left), height(node.right)) + 1;
return node;

}

public Integer search(Node<T> node , T value){
if(node == null)
return -1 ;
int comparaResult = value.compareTo(node.value);
if(comparaResult == 0)
return node.position;
else if(comparaResult > 0)
return search(node.right, value);
else if(comparaResult < 0)
return search(node.left, value);
else
return -1;
}

private void preorder(Node<T> node){
if(null == node)
return ;
System.out.print(node.value);
preorder(node.left);
preorder(node.right);
}

private void midorder(Node<T> node){
if(null == node)
return ;
midorder(node.left);
System.out.print(node.value);
midorder(node.right);
}

private void postorder(Node<T> node){
if(null == node)
return ;
postorder(node.left);
postorder(node.right);
System.out.print(node.value);
}

public static void main(String[] args){
BST<Integer> bst = new BST<Integer>();
int[] array = {0,1,5,6,7,2,3,4,8,9};
for(int i=0;i<array.length;i++)
bst.add(array[i],i);//
System.out.println(bst.height(bst.root));
System.out.println(bst.search(bst.root, 8));
System.out.println(bst.search(bst.root, 0));
System.out.println(bst.search(bst.root, 22));

bst.preorder(bst.root);
System.out.println();
bst.midorder(bst.root);
System.out.println();
bst.postorder(bst.root);
}
}