题解 | #序列化二叉树#

/*class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 * 
 * @param root TreeNode类 
 * @return TreeNode类
 */
//二叉树的序列化和反序列化
//序列化:前序遍历、中序遍历、后序遍历
//反序列化:前序遍历、后序遍历
// const result = []
// const NULL = '#'
// const str = ','    
// export function Serialize(root: TreeNode): string { 
//     if(root == null){
//         result.push(NULL)
//         return
//     }
//     //前序遍历
//     result.push(root.val)
//     result.push(str)
//     Serialize(root.left)
//     result.push(str)
//     Serialize(root.right)
//     return result.join("")
// }
// export function Deserialize(str: string): TreeNode {
//   // 还原为二叉树
//   //转化为数组
//   if(str.length == 0)return null
//   const array = str.split(',')
//   const first = array.shift()
//   if(first == NULL)return null
//   const root = new TreeNode(Number(first))
//   root.left = Deserialize(array.join(","))
//   root.right = Deserialize(array.join(","))
//   return root
// }

const result = []  
const NULL = '#'  
  
export function Serialize(root: TreeNode): string {   
    if (root === null) {
        result.push(NULL);
        result.push(',');
        return result.join("");  
    }
    // 前序遍历
    result.push(root.val);
    result.push(',');
    Serialize(root.left);
    Serialize(root.right);
    return result.join("");
}  
  
export function Deserialize(str: string): TreeNode {  
  // 还原为二叉树  
  //转化为数组  
   if (str.length === 0) return null;
    const array = str.split(',');

    function buildTree(): TreeNode {
        if(array.length == 0)return null
        const first = array.shift();
        if (first === NULL) return null;
        const root = new TreeNode(Number(first));
        root.left = buildTree();
        root.right = buildTree();
        return root;
    }
      return buildTree();
}