Android 数据结构之 二叉树

最近抽时间看了下二叉树，下面把二叉树的相关遍历方式共享下
1.定义树结构类

 public class TreeNode {
    public TreeNode left;

    public TreeNode getLeft() {
        return left;
    }

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

    public TreeNode getRight() {
        return right;
    }

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

    public int getVal() {
        return val;
    }

    public void setVal(int val) {
        this.val = val;
    }

    public TreeNode right;
    public int val ;
}

2.创建二叉树

public void test(){
        TreeNode treeNode = new TreeNode();
        treeNode.setVal(0);
        TreeNode treeNode1 = new TreeNode();
        treeNode1.setVal(1);
        TreeNode treeNode2 = new TreeNode();
        treeNode2.setVal(2);
        treeNode.setLeft(treeNode1);
        treeNode.setRight(treeNode2);
        TreeNode treeNode3 = new TreeNode();
        treeNode3.setVal(3);
        TreeNode treeNode4 = new TreeNode();
        treeNode4.setVal(4);
        treeNode1.setLeft(treeNode3);
        treeNode1.setRight(treeNode4);
        TreeNode treeNode5 = new TreeNode();
        treeNode5.setVal(5);
        TreeNode treeNode6 = new TreeNode();
        treeNode6.setVal(6);
        treeNode2.setLeft(treeNode5);
        treeNode2.setRight(treeNode6);
        TreeNode treeNode7 = new TreeNode();
        treeNode7.setVal(7);
        TreeNode treeNode8 = new TreeNode();
        treeNode8.setVal(8);
        treeNode3.setLeft(treeNode7);
        treeNode3.setRight(treeNode8);
        //前序
        preOrderTraverse(treeNode);
        //中序
        inOrderTraverse(treeNode);
        //后序
        postOrderTraverse(treeNode);
    }

  /*二叉树的前序遍历递归算法*/
    private void preOrderTraverse(TreeNode treeNode){
        if(treeNode==null)return;
        Log.e("MainActivity","preOrderTraverse--val:"+treeNode.val);
        preOrderTraverse(treeNode.left);
        preOrderTraverse(treeNode.right);
    }

    /*二叉树的中序遍历递归算法*/
    void inOrderTraverse(TreeNode treeNode)
    {
        if(treeNode==null)return;
        inOrderTraverse(treeNode.left); /*中序遍历左子树*/
        Log.e("MainActivity","inOrderTraverse--val:"+treeNode.val);
        inOrderTraverse(treeNode.right); /*最后中序遍历右子树*/
    }

    /*二叉树的后序遍历递归算法*/
    void postOrderTraverse(TreeNode treeNode)
    {
        if(treeNode==null)return;
        postOrderTraverse(treeNode.left); /*先后遍历左子树*/
        postOrderTraverse(treeNode.right); /*在后序遍历右子树*/
        Log.e("MainActivity","postOrderTraverse---val:"+treeNode.val);
    }