JS 二叉搜索樹 - 筆記

Code:

class TreeNode {
    val;
    left;
    right;
    constructor(val, left, right) {
        this.val = val ?? 0;
        this.left = left ? left : null;
        this.right = right ? right : null;
    }
}

/**
 * 二叉搜索樹
 */
class BinarySearchTree {
    /**
     * @type {TreeNode}
     */
    #root;

    /**
     * @constructor
     */
    constructor() {
        this.#root = null;
    }

    getRoot() {
        return this.#root;
    }

    /**
     * 插入新節點
     * @param {number} num 
     */
    insert(num) {
        if (this.#root === null) {
            this.#root = new TreeNode(num);
            return;
        }

        let prev = null;
        let cur = this.#root;

        // 到達葉子節點後退出
        while (cur !== null) {
            // 已經存在某個節點的值與待插入的新值相等
            if (cur.val === num) {
                return;
            }
            prev = cur;
            // 插入值比當前節點的值要大
            if (num > cur.val) {
                cur = cur.right;
            }
            // 比當前值小
            else {
                cur = cur.left;
            }
        }

        const node = new TreeNode(num);
        if (num > prev.val) {
            prev.right = node;
        }
        else {
            prev.left = node;
        }
    }

    /**
     * 查找節點
     * @param {number} num
     * @returns {TreeNode}
     */
    search(num) {
        let cur = this.#root;
        while (cur !== null) {
            if (cur.val < num) {
                cur = cur.right;
            }
            else if (cur.val > num) {
                cur = cur.left;
            }
            else {
                break;
            }
        }

        return cur;
    }

    /**
     * 刪除節點
     * @param {number} num 
     * @returns 
     */
    remove(num) {
        if (this.#root === null) {
            return;
        }

        let prev = null;
        let cur = this.#root;

        while (cur !== null) {
            if (cur.val === null) {
                break;
            }
            prev = cur;
            if (cur.val < num) {
                cur = cur.right;
            }
            else {
                cur = cur.left;
            }
        }

        if (cur === null) {
            return;
        }

        //// 子節點數量爲 0 或者 1
        if (cur.left === null || cur.right === null) {
            const child = cur.left === null ? cur.right ? cur.left;
            if (cur === this.#root) {
                this.#root = child;
            }
            else {
                if (prev.left === cur) {
                    prev.left = child;
                }
                else {
                    prev.right = child;
                }
            }
        }
        //// 子節點數量爲 2
        else {
            let tmp = cur.right;
            while (tmp.left !== null) {
                tmp = tmp.left;
            }
            this.remove(tmp.val);
            cur.val = tmp.val;
        }
    }
}