本文介绍: 树的三种遍历 前序,中序,后序

题目

树的三种遍历方式,前序,中序,后续

解题

通过递归

public static List<Integer> preorderTraversal(TreeNode treeNode) {
    List<Integer> result = new ArrayList<>();
    if (treeNode == null) {
      return result;
    }
    List<Integer> left = preorderTraversal(treeNode.left);
    List<Integer> right = preorderTraversal(treeNode.right);
    result.add(treeNode.getValue());
    result.addAll(left);
    result.addAll(right);

    return result;
  }

  public static List<Integer> midorderTraversal(TreeNode treeNode) {
    List<Integer> result = new ArrayList<>();
    if (treeNode == null) {
      return result;
    }
    List<Integer> left = midorderTraversal(treeNode.left);
    List<Integer> right = midorderTraversal(treeNode.right);
    result.addAll(left);
    result.add(treeNode.getValue());
    result.addAll(right);

    return result;
  }

  public static List<Integer> backorderTraversal(TreeNode treeNode) {
    List<Integer> result = new ArrayList<>();
    if (treeNode == null) {
      return result;
    }
    List<Integer> left = backorderTraversal(treeNode.left);
    List<Integer> right = backorderTraversal(treeNode.right);
    result.addAll(left);
    result.addAll(right);
    result.add(treeNode.getValue());

    return result;
  }

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