BinaryTreePruning.js

// Source : https://leetcode.com/problems/binary-tree-pruning
// Author : Dean Shi
// Date   : 2018-04-15

/***************************************************************************************
 * We are given the head node root of a binary tree, where additionally every node's
 * value is either a 0 or a 1.
 *
 * Return the same tree where every subtree (of the given tree) not containing a 1 has
 * been removed.
 *
 * (Recall that the subtree of a node X is X, plus every node that is a descendant of X.
 * )
 *
 * Example 1:
 * Input: [1,null,0,0,1]
 * Output: [1,null,0,null,1]
 *
 * Explanation:
 * Only the red nodes satisfy the property "every subtree not containing a 1".
 * The diagram on the right represents the answer.
 *
 * Example 2:
 * Input: [1,0,1,0,0,0,1]
 * Output: [1,null,1,null,1]
 *
 * Example 3:
 * Input: [1,1,0,1,1,0,1,0]
 * Output: [1,1,0,1,1,null,1]
 *
 * Note:
 *
 * The binary tree will have at most 100 nodes.
 * The value of each node will only be 0 or 1.
 *
 ***************************************************************************************/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {TreeNode}
 */
var pruneTree = function(root) {
    if (!root) return root

    root.left = pruneTree(root.left)
    root.right = pruneTree(root.right)

    return root.left === null && root.right === null && root.val === 0
        ? null
        : root
};