Skip to main content

Construct String from Binary Tree

Problem statement​

Given the root of a binary tree, construct a string consisting of parenthesis and integers from a binary tree with the preorder traversal way, and return it.

Omit all the empty parenthesis pairs that do not affect the one-to-one mapping relationship between the string and the original binary tree.

Example 1:

Input: root = [1,2,3,4]Output: "1(2(4))(3)"Explanation: Originally, it needs to be "1(2(4)())(3()())", but you need to omit all the unnecessary empty parenthesis pairs. And it will be "1(2(4))(3)"

Example 2:

Input: root = [1,2,3,null,4]Output: "1(2()(4))(3)"Explanation: Almost the same as the first example, except we cannot omit the first parenthesis pair to break the one-to-one mapping relationship between the input and the output.

Constraints:

  • The number of nodes in the tree is in the range [1, 104].
  • -1000 <= Node.val <= 1000

My solution​

/**
 * 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)
 * }
 */
/**
 * @param {TreeNode} t
 * @return {string}
 */
var tree2str = function(t) {
    if (!t) {
        return "";
    }
    
    const val = t.val;
    const left = tree2str(t.left);
    const right = tree2str(t.right);
    
    // console.log("left", left, val);
    // console.log("right", right, val);
    
    if (!left && !right) {
        return `${val}`;
    }
    
    if (!right) {
        return `${val}(${left})`;
    }
    
    return `${val}(${left})(${right})`;
};