判断对称二叉树

type TreeNode = {
    val: any;
    left: TreeNode;
    right: TreeNode;
};

function createTreeNode(val: any = null, left: TreeNode = null, right: TreeNode = null) : TreeNode {
    const node: TreeNode = {val, left, right};
    return node;
}

/**
 * 构造二叉树
 * @param preArray 前序遍历列表
 * @param inArray 中序遍历列表
 * @returns 二叉树根节点
 */
function makeTree(preArray: any[], inArray: any[]) : TreeNode {
    if (!preArray.length) return null;
    const val = preArray[0];
    const node = createTreeNode(val);
    const index = inArray.indexOf(val);
    node.left = makeTree(preArray.slice(1, 1 + i), inArray.slice(0, i));
    node.right = makeTree(preArray.slice(i + 1), inArray.slice(i + 1));
    return node;
}

/**
 * 判断二叉树是否为对称二叉树
 * @param tree 二叉树根节点
 * @returns 是否为对称二叉树
 */
function isSymmetricTree(tree: TreeNode) : boolean {
    if (!tree) return true;
    const dfs = function(l: TreeNode, r: TreeNode) : boolean {
        if (l === null && r === null) return true;
        if (l && r) {
            if (l.val !== r.val) return false;
            if (dfs(l.left, r.right) && dfs(l.right, r.left)) return true;
        }
        return false;
    };
    return dfs(tree.left, tree.right);
}

const preArray = [1, 2, 3, 2, 3];
const inArray = [3, 2, 1, 2, 3];
const tree = makeTree(preArray, inArray);
console.log(isSymmetricTree(tree));