二叉树遍历算法实现（递归、非递归）

二叉树遍历可采用前序遍历（先根遍历）、中序遍历、后序遍历。具体实现算法包括递归和非递归。

package Tree;import java.util.Stack;/** *  * @ClassName: BinaryTree * * @Description: 二叉树相关算法实现 * * @author: ccding * @date: 2017年5月24日 下午8:20:13 * * @param <T> */public class BinaryTree <T extends Comparable <T>> {    public TreeNode<T> root;// root node of binary tree    //construct method    public BinaryTree(TreeNode<T> root){        this.root = root;    }    /**     * 先序遍历递归实现     */    public void preOrderTraverse(TreeNode<T> t){        if(t != null){            System.out.print(t.val+" ");            preOrderTraverse(t.left);            preOrderTraverse(t.right);        }    }    /**     * 先序遍历非递归实现     */    public void preOrderTraverseII(TreeNode<T> t){        Stack<TreeNode<T>> s = new Stack<>();        s.push(t);        TreeNode<T> curr = t;        while(!s.isEmpty() || curr!=null){            while(curr!=null){                System.out.print(curr.val + " ");                s.push(curr);                curr = curr.left;            }            if(!s.isEmpty()){                curr = s.pop();                curr = curr.right;            }        }    }    /**     * 先序遍历非递归实现     */    public void preOrderTraverseIII(TreeNode<T> t){        Stack<TreeNode<T>> s = new Stack<>();        s.push(t);        TreeNode<T> p = null;        while(!s.isEmpty()){            p = s.pop();            System.out.print(p.val + " ");            if(p.right != null)                s.push(p.right);            if(p.left != null)                s.push(p.left);        }    }    /**     * 中序遍历递归实现     */    public void inOrderTraverse(TreeNode<T> t){        if(t != null){            inOrderTraverse(t.left);            System.out.print(t.val+" ");            inOrderTraverse(t.right);        }    }    /**     * 中序遍历非递归实现     */    public void inOrderTraverseII(TreeNode<T> t){        Stack<TreeNode<T>> s = new Stack<>();        TreeNode<T> curr = t;        while(!s.isEmpty() || curr!=null){            while(curr != null){                s.push(curr);                curr = curr.left;            }            if(!s.isEmpty()){                curr = s.pop();                System.out.print(curr.val + " ");                curr = curr.right;            }        }    }    /**     * 后序遍历递归实现     */    public void postOrderTraverse(TreeNode<T> t){        if(t != null){            postOrderTraverse(t.left);            postOrderTraverse(t.right);            System.out.print(t.val+" ");        }    }    /**     * 后序遍历非递归实现     */    public void postOrderTraverseII(TreeNode<T> t){        Stack<TreeNode<T>> s1 = new Stack<>();        Stack<TreeNode<T>> s2 = new Stack<>();        s1.push(t);        TreeNode<T> curr = null;        while(!s1.isEmpty()){            curr = s1.pop();            s2.push(curr);            if(curr.left!=null)                s1.push(curr.left);            if(curr.right != null)                s1.push(curr.right);        }        while(!s2.isEmpty())            System.out.print(s2.pop().val + " ");    }}