二叉树按层遍历

Posted 2020-10-12

/*         
 * 二叉树的层次遍历      
 *     1.首先将根节点放入队列中。 
       2.当队列为非空时，循环执行步骤3到步骤5，否则执行6； 
       3.出队列取得一个结点，访问该结点； 
       4.若该结点的左子树为非空，则将该结点的左子树入队列； 
       5.若该结点的右子树为非空，则将该结点的右子树入队列； 
       6.结束。
  */  

import java.util.Queue;

public class BinaryTree<T> {
    private T data;
    private BinaryTree<T> left;
    private BinaryTree<T> right;
    
    private BinaryTree(T data) {
        this.data = data;
    }
    public BinaryTree() {
        
    }
    //层次遍历
    public static void levelTraverse(BinaryTree root) {
        if(root==null) {
            try {
                throw new Exception("二叉树为空");
            }catch (Exception e) {
                e.printStackTrace();
            }
        }else {
            Queue<BinaryTree> queue = new Queue<BinaryTree>();
            
            queue.enqueue(root);
            while(!queue.isEmpty()) {
                root = queue.dequeue();
                System.out.print(root.data + " ");
                if(root.left != null)
                    queue.enqueue(root.left);
                if(root.right != null)
                    queue.enqueue(root.right);                
            }
        }
    }
    //换行层次遍历
    public static void newLevelTraverse(BinaryTree root) {
        BinaryTree last = new BinaryTree();
        BinaryTree nlast = new BinaryTree();
        if(root==null) {
            try {
                throw new Exception("二叉树为空");
            }catch (Exception e) {
                e.printStackTrace();
            }
        }else {
            Queue<BinaryTree> queue = new Queue<BinaryTree>();
            
            queue.enqueue(root);
            last = root;//last表示正在打印的当前行 的最右节点
            nlast = root;//nlast表示下一行的最右节点，nlast节点每次跟踪记录最先加入队列的节点
            
            while(!queue.isEmpty()) {                                
                root = queue.dequeue();
                System.out.print(root.data+" ");
                if(root.left != null) {
                    queue.enqueue(root.left);
                    nlast = root.left;
                }                    
                if(root.right != null) {
                    queue.enqueue(root.right);
                    nlast = root.right;
                }
                //如果当前输出节点root是最右节点last,那么换行
                if(last == root) {
                    System.out.println();
                    last = nlast;//last节点更新为nlast节点
                }
            }
        }
        
        
        
    }
    public static void main(String[] args) {
        BinaryTree b1 = new BinaryTree(1);
        BinaryTree b2 = new BinaryTree(2);
        BinaryTree b3 = new BinaryTree(3);
        BinaryTree b4 = new BinaryTree(4);
        BinaryTree b5 = new BinaryTree(5);
        BinaryTree b6 = new BinaryTree(6);
        BinaryTree b7 = new BinaryTree(7);
        BinaryTree b8 = new BinaryTree(8);
        
        b1.left = b2;
        b1.right = b3;
        b2.left = b4;
        b3.left = b5;
        b3.right = b6;
        b5.left = b7;
        b5.right = b8;
        //层次遍历二叉树
        BinaryTree.levelTraverse(b1);
　　　　　//换行层次遍历
        BinaryTree.newLevelTraverse(b1);
    }
}