二叉树的递归与非递归遍历

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构造树如下:

其中二叉树节点类

/** 二叉树节点 */
public class BTNode {
     private char key;
     private BTNode left, right;

     public BTNode( char key) {
         this(key, null, null);
    }

     public BTNode( char key, BTNode left, BTNode right) {
         this.key = key;
         this.left = left;
         this.right = right;
    }

     public char getKey() {
         return key;
    }

     public void setKey( char key) {
         this.key = key;
    }

     public BTNode getLeft() {
         return left;
    }

     public void setLeft(BTNode left) {
         this.left = left;
    }

     public BTNode getRight() {
         return right;
    }

     public void setRight(BTNode right) {
         this.right = right;
    }
}

遍历二叉树

/** 二叉树遍历 */
public class BinTree {
     protected BTNode root;

     public BinTree(BTNode root) {
         this .root = root;
    }

     public BTNode getRoot() {
         return root;
    }

     /** 构造树 */
     public static BTNode init() {
        BTNode a = new BTNode('A');
        BTNode b = new BTNode('B', null , a);
        BTNode c = new BTNode('C');
        BTNode d = new BTNode('D', b, c);
        BTNode e = new BTNode('E');
        BTNode f = new BTNode('F', e, null );
        BTNode g = new BTNode('G', null , f);
        BTNode h = new BTNode('H', d, g);
         return h; // root
    }

     /** 访问节点 */
     public static void visit(BTNode p) {
        System.out.print(p.getKey() + " " );
    }

     /** 递归实现前序遍历 */
     protected static void preorder(BTNode p) {
         if (p != null ) {
            visit(p);
            preorder(p.getLeft());
            preorder(p.getRight());
        }
    }

     /** 递归实现中序遍历 */
     protected static void inorder(BTNode p) {
         if (p != null ) {
            inorder(p.getLeft());
            visit(p);
            inorder(p.getRight());
        }
    }

     /** 递归实现后序遍历 */
     protected static void postorder(BTNode p) {
         if (p != null ) {
            postorder(p.getLeft());
            postorder(p.getRight());
            visit(p);
        }
    }

     /** 非递归实现前序遍历 */
     protected static void iterativePreorder(BTNode p) {
        Stack stack = new Stack();
         if (p != null ) {
            stack.push(p);
             while (!stack.empty()) {
                p = stack.pop();
                visit(p);
                 if (p.getRight() != null )
                    stack.push(p.getRight());
                 if (p.getLeft() != null )
                    stack.push(p.getLeft());
            }
        }
    }

     /** 非递归实现后序遍历 */
     protected static void iterativePostorder(BTNode p) {
        BTNode q = p;
        Stack stack = new Stack();
         while (p != null ) {
             // 左子树入栈
             for (; p.getLeft() != null ; p = p.getLeft())
                stack.push(p);
             // 当前节点无右子或右子已经输出
             while (p != null && (p.getRight() == null || p.getRight() == q)) {
                visit(p);
                q = p; // 记录上一个已输出节点
                 if (stack.empty())
                     return ;
                p = stack.pop();
            }
             // 处理右子
            stack.push(p);
            p = p.getRight();
        }
    }

     /** 非递归实现中序遍历 */
     protected static void iterativeInorder(BTNode p) {
        Stack stack = new Stack();
         while (p != null ) {
             while (p != null ) {
                 if (p.getRight() != null )
                    stack.push(p.getRight()); // 当前节点右子入栈
                stack.push(p); // 当前节点入栈
                p = p.getLeft();
            }
            p = stack.pop();
             while (!stack.empty() && p.getRight() == null ) {
                visit(p);
                p = stack.pop();
            }
            visit(p);
             if (!stack.empty())
                p = stack.pop();
             else
                p = null ;
        }
    }

     public static void main(String[] args) {
        BinTree tree = new BinTree(init());
        System.out.print( " Pre-Order:" );
        preorder(tree.getRoot());
        System.out.println();
        System.out.print( "  In-Order:" );
        inorder(tree.getRoot());
        System.out.println();
        System.out.print( "Post-Order:" );
        postorder(tree.getRoot());
        System.out.println();
        System.out.print( " Pre-Order:" );
        iterativePreorder(tree.getRoot());
        System.out.println();
        System.out.print( "  In-Order:" );
        iterativeInorder(tree.getRoot());
        System.out.println();
        System.out.print( "Post-Order:" );
        iterativePostorder(tree.getRoot());
        System.out.println();
    }
}

输出结果
 Pre-Order:H D B A C G F E
  In-Order:B A D C H G E F
Post-Order:A B C D E F G H
 Pre-Order:H D B A C G F E
  In-Order:B A D C H G E F
Post-Order:A B C D E F G H 

本文出自 “子 孑” 博客，请务必保留此出处http://zhangjunhd.blog.51cto.com/113473/82616