701.二叉搜索树中的插入操作

function TreeNode(val, left, right) {
    this.val = (val === undefined ? 0 : val)
    this.left = (left === undefined ? null : left)
    this.right = (right === undefined ? null : right)
}

/**
 * @param {TreeNode} root
 * @param {number} val
 * @return {TreeNode}
 */
var insertIntoBST = function (root, val) {
    let newNode = new TreeNode(val)
    if(!root) {
        root = newNode
        return root
    }
    let cur = root
    // 左节点<父节点<右节点，根据这个规律找到合适的叶子节点
    while (true) {
        if (val < cur.val) {
            if (cur.left === null) {
                cur.left = newNode
                break
            }
            cur = cur.left
        } else {
            if (cur.right === null) {
                cur.right = newNode
                break
            }
            cur = cur.right
        }
    }

    return root
};