653.两数之和-输入二叉搜索树

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * 给定一个二叉搜索树 root 和一个目标结果 k，如果二叉搜索树中存在两个元素且它们的和等于给定的目标结果，则返回 true。
 * @param {TreeNode} root
 * @param {number} k
 * @return {boolean}
 */
var findTarget = function (root, k) {
    // 找差值，target = k - node.val
    // 使用层序遍历
    let targets = []
    let queue = []
    queue.push(root)
    while (queue.length) {
        let len = queue.length // 每一层的节点数
        for (let i = 0; i < len; i++) {
            let node = queue.shift()
            if (targets.includes(node.val)) {
                return true
            } else {
                targets.push(k - node.val)
            }

            if (node.left) {
                queue.push(node.left)
            }
            if (node.right) {
                queue.push(node.right)
            }
        }
    }
    return false
};

// 递归
var findTarget = function (root, k) {
    let targets = [] // 差值队列
    // 前序，中左右
    function preorder(node) {
        if (node === null) {
            return false
        }
        console.log(node.val);
        if (targets.includes(node.val)) {
            return true
        } else {
            targets.push(k - node.val)
        }
        let left = preorder(node.left)
        let right = preorder(node.right)
        return left || right
    }
    return preorder(root)
}