java数据结构之二叉树遍历的非递归实现

Posted 2020-09-20 牛头人

算法概述
递归算法简洁明了、可读性好，但与非递归算法相比要消耗更多的时间和存储空间。为提高效率，我们可采用一种非递归的二叉树遍历算法。非递归的实现要借助栈来实现，因为堆栈的先进后出的结构和递归很相似。
对于中序遍历来说，非递归的算法比递归算法的效率要高的多。其中序遍历算法的实现的过程如下：
(1).初始化栈，根结点进栈；
(2).若栈非空，则栈顶结点的左孩子结点相继进栈，直到null(到叶子结点时)退栈；访问栈顶结点(执行visit操作)并使栈顶结点的右孩子结点进栈成为栈顶结点。
(3).重复执行(2)，直至栈为空。
算法实现
    package datastructure.tree;  
      
    import datastructure.stack.ArrayStack;  
    import datastructure.stack.Stack;  
      
    public class UnrecOrderBTree implements Visit{  
        private Stack stack = new ArrayStack();  
        private BTree bt;  
        @Override  
        public void visit(BTree btree) {  
            System.out.print("\\t" + btree.getRootData());  
        }  
          
        public void inOrder(BTree boot) {  
            stack.clear();  
            stack.push(boot);  
            while(!stack.isEmpty()) {  
                //左孩子结点进栈  
                while((bt = ((BTree)(stack.peek())).getLeftChild()) != null) {  
                    stack.push(bt);  
                }  
                //如果该结点没有右孩子，则逐级往上出栈  
                while(!stack.isEmpty() &&!( (BTree)stack.peek() ).hasRightTree()) {  
                    bt = (BTree)stack.pop();  
                    visit(bt);  
                }  
                //如果该结点有右孩子，则右孩子进栈  
                if(!stack.isEmpty() && ( (BTree)stack.peek() ).hasRightTree()){  
                    bt = (BTree)stack.pop();  
                    visit(bt);  
                    stack.push(bt.getRightChild());  
                }  
            }  
        }  
      
    }  
测试：

 

    package datastructure.tree;  
    /**
     * 测试二叉树
     * @author Administrator
     *
     */  
    public class BTreeTest {  
        public static void main(String args[]) {  
            BTree btree = new LinkBTree(\'A\');  
            BTree bt1, bt2, bt3, bt4;  
            bt1 = new LinkBTree(\'B\');  
            btree.addLeftTree(bt1);  
            bt2 = new LinkBTree(\'D\');  
            bt1.addLeftTree(bt2);  
              
            bt3 =  new LinkBTree(\'C\');  
            btree.addRightTree(bt3);  
            bt4 =  new LinkBTree(\'E\');  
            bt3.addLeftTree(bt4);  
            bt4 =  new LinkBTree(\'F\');  
            bt3.addRightTree(bt4);  
              
            RecursionOrderBTree order = new RecursionOrderBTree();  
            System.out.println("\\n中序遍历：");  
            order.inOrder(btree);  
              
        }  
    }  

结果如下：
中序遍历：
D B  A E
C   F

 

转载至：http://blog.csdn.net/luoweifu/article/details/9079799