图解二叉树的三种遍历方式及java实现代码

  // 定义节点类：
  private static class BinNode {
    private Object element;
    private BinNode lChild;// 定义指向左子树的指针
    private BinNode rChild;// 定义指向右子树的指针

    public BinNode(Object element, BinNode lChild, BinNode rChild) {
      this.element = element;
      this.lChild = lChild;
      this.rChild = rChild;
    }
  }

  /**
   * 对该二叉树进行前序遍历 结果存储到list中 前序遍历
   */
  public static void preOrder(BinNode node) {
    list.add(node); // 先将根节点存入list
    // 如果左子树不为空继续往左找，在递归调用方法的时候一直会将子树的根存入list，这就做到了先遍历根节点
    if (node.lChild != null) {
      preOrder(node.lChild);
    }
    // 无论走到哪一层，只要当前节点左子树为空，那么就可以在右子树上遍历，保证了根左右的遍历顺序
    if (node.rChild != null) {
      preOrder(node.rChild);
    }
  }

  /**
   * 对该二叉树进行中序遍历 结果存储到list中
   */
  public static void inOrder(BinNode node) {
    if (node.lChild != null) {
      inOrder(node.lChild);
    }
    list.add(node);
    if (node.rChild != null) {
      inOrder(node.rChild);
    }
  }

  /**
   * 对该二叉树进行后序遍历 结果存储到list中
   */
  public static void postOrder(BinNode node) {
    if (node.lChild != null) {
      postOrder(node.lChild);
    }
    if (node.rChild != null) {
      postOrder(node.rChild);
    }
    list.add(node);
  }

  private static BinNode root;
  private static List<BinNode> list = new ArrayList<BinNode>();

  public static void main(String[] args) {
    init();
    // TODO Auto-generated method stub
    //preOrder(root);
    //inOrder(root);
    postOrder(root);
    for (int i = 0; i < list.size(); i++) {
      System.out.print(list.get(i).element + " ");
    }
  }

  // 树的初始化:先从叶节点开始,由叶到根
  public static void init() {
    BinNode b = new BinNode("b", null, null);
    BinNode a = new BinNode("a", null, b);
    BinNode c = new BinNode("c", a, null);

    BinNode e = new BinNode("e", null, null);
    BinNode g = new BinNode("g", null, null);
    BinNode f = new BinNode("f", e, g);
    BinNode h = new BinNode("h", f, null);

    BinNode d = new BinNode("d", c, h);

    BinNode j = new BinNode("j", null, null);
    BinNode k = new BinNode("k", j, null);
    BinNode m = new BinNode("m", null, null);
    BinNode o = new BinNode("o", null, null);
    BinNode p = new BinNode("p", o, null);
    BinNode n = new BinNode("n", m, p);
    BinNode l = new BinNode("l", k, n);

    root = new BinNode("i", d, l);
  }