二叉树的遍历

遍历：按照一定的顺序访问（可以是打印节点值，可以是计算节点个数）这个集合中的所有元素做到不重漏。

 二叉树的三种遍历实现的代码：

package datastructure.bin_tree;

public class MyBinTree {
    private static class TreeNode {
        E val;
        TreeNode left;
        TreeNode right;

        public TreeNode(E val) {
            this.val = val;
        }

    }

    //创建一个二叉树返回根节点
    public static TreeNode build() {
        TreeNode nodeA = new TreeNode('A');
        TreeNode nodeB = new TreeNode('B');
        TreeNode nodeC = new TreeNode('C');
        TreeNode nodeD = new TreeNode('D');
        TreeNode nodeE = new TreeNode('E');
        TreeNode nodeF = new TreeNode('F');
        TreeNode nodeG=new TreeNode('G');
        nodeA.left=nodeB;
        nodeA.right=nodeC;
        nodeB.left=nodeD;
        nodeB.right=nodeE;
        nodeC.left=nodeF;
        nodeC.right=nodeG;
        return nodeA;
    }
//二叉树的先序遍历
//根左右
public static void preOrder(TreeNode root){
        if(root==null){
            return;
        }
    System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
}
public static void inOrder(TreeNode root){
        if (root==null){
            return;
        }
   inOrder(root.left);
    System.out.print(root.val+" ");
    inOrder(root.right);
}
public static void postOrder(TreeNode root){
        if (root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
    System.out.print(root.val+" ");
}

    public static void main(String[] args) {
        TreeNode root=build();
        System.out.print("先序遍历的结果：");
        preOrder(root);
        System.out.println();
        System.out.print("中序遍历的结果是：");
        inOrder(root);
        System.out.println();
        System.out.print("后序遍历的结果是：");
        postOrder(root);

    }
}

最终的运行结果：