数据结构与算法-04二叉树-02

链表方式构建二叉搜索树

Binary Search Tree

• 二叉树： 最多有两个子节点
• 左小右大； BST的特点

构建节点

节点构成

一般节点有三部分构成:

1. 节点的数据 val
2. 节点的左子节点 left
3. 节点的右子节点 right

节点实现

public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;

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

    public TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }

    @Override
    public String toString() {
        return "TreeNode{" +
                "val=" + val +
                ", left=" + left +
                ", right=" + right +
                '}';
    }
}

添加节点（链表)

循环方式构建

• 如果无根节点，新节点就是根节点。
• 与节点的左、右节点值比较。

 public void insert(int val) {
        TreeNode newNode = new TreeNode(val);

        if(root == null) {
            root = newNode;
            return;
        }
        TreeNode curr = root;
        while (curr != null) {
            if (val > curr.val) {
                if (curr.right == null) {
                    curr.right = newNode;
                    return;
                }
                curr = curr.right;
            } else {
                if (curr.left == null) {
                    curr.left = newNode;
                    return;
                }
                curr = curr.left;
            }
        }
    }

递归方式构建

public TreeNode insert(TreeNode root, int val) {
    TreeNode newNode = new TreeNode(val);
    if (root == null) {
        root = newNode;
        return root;
    }
    if (val > root.val) {
        root.right = insert(root.right, val);
    }
    if (val < root.val) {
        root.left = insert(root.left, val);
    }
    return root;
}