Java搜索树

概念

二叉搜索树又称二叉排序树，它或者是一棵空树**，或者是具有以下性质的二叉树：

操作

搜索树的操作有搜索，插入，删除，其中删除操作最为复杂：

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

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

    public  TreeNode root ;

    public  boolean search(int val) {
        if(root == null) {
            return false;
        }
        TreeNode cur = root;
        while (cur != null) {
            if(cur.val == val) {
                return true;
            }else if(cur.val > val) {
                cur = cur.left;
            }else {
                cur = cur.right;
            }
        }
        return false;
    }

    public  boolean insert(int val) {
        if(root == null) {
            root = new TreeNode(val);
            return true;
        }
        TreeNode cur = root;
        TreeNode parent = null;
        while (cur != null) {
            if(cur.val < val) {
                parent = cur;
                cur = cur.right;
            }else if(cur.val > val) {
                parent = cur;
                cur = cur.left;
            }else {
                return false;//不能插入相同的数字
            }
        }
        if(parent.val < val) {
            parent.right = new TreeNode(val);;
        }else {
            parent.left = new TreeNode(val);;
        }
        return true;
    }

    public boolean remove(int key) {
        if(root == null) {
            return false;
        }
        TreeNode cur = root;
        TreeNode parent = null;
        while (cur != null) {
            if(cur.val < key) {
                parent = cur;
                cur = cur.right;
            }else if (cur.val > key) {
                parent = cur;
                cur = cur.left;
            }else {
                removeNode(parent,cur);
                return true;
            }
        }
        return false;
    }

    public void removeNode(TreeNode parent,TreeNode cur) {
        if(cur.left == null) {
            if(cur == root) {
                root = cur.right;
            }else if(parent.right == cur) {
                parent.right = cur.right;
            }else {
                parent.left = cur.right;
            }
        }else if(cur.right == null) {
            if(cur == root) {
                root = cur.left;
            }else if(parent.left == cur) {
                parent.left = cur.left;
            }else {
                parent.right = cur.left;
            }
        }else {
            TreeNode target = cur.right;
            TreeNode targetParent = cur;
            while (target.left != null) {
                targetParent = target;
                target = target.left;
            }
            cur.val = target.val;
            if(target == targetParent.left) {
                targetParent.left = target.right;
            }else {
                targetParent.right = target.right;
            }
        }
    }
}