Problem
You are given a 2D integer array descriptions
where descriptions[i] = [parenti, childi, isLefti]
indicates that parenti
is the parent of childi
in a binary tree of unique values. Furthermore,
If
isLefti == 1
, thenchildi
is the left child ofparenti
.If
isLefti == 0
, thenchildi
is the right child ofparenti
.
Construct the binary tree described by descriptions
and return **its *root***.
The test cases will be generated such that the binary tree is valid.
Example 1:
Input: descriptions = [[20,15,1],[20,17,0],[50,20,1],[50,80,0],[80,19,1]]
Output: [50,20,80,15,17,19]
Explanation: The root node is the node with value 50 since it has no parent.
The resulting binary tree is shown in the diagram.
Example 2:
Input: descriptions = [[1,2,1],[2,3,0],[3,4,1]]
Output: [1,2,null,null,3,4]
Explanation: The root node is the node with value 1 since it has no parent.
The resulting binary tree is shown in the diagram.
Constraints:
1 <= descriptions.length <= 104
descriptions[i].length == 3
1 <= parenti, childi <= 105
0 <= isLefti <= 1
The binary tree described by
descriptions
is valid.
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 {number[][]} descriptions
* @return {TreeNode}
*/
var createBinaryTree = function(descriptions) {
var nodeMap = {};
var hasNoParentMap = {};
for (var i = 0; i < descriptions.length; i++) {
var [parent, child, isLeft] = descriptions[i];
if (hasNoParentMap[parent] === undefined) hasNoParentMap[parent] = true;
hasNoParentMap[child] = false;
if (!nodeMap[parent]) nodeMap[parent] = new TreeNode(parent);
if (!nodeMap[child]) nodeMap[child] = new TreeNode(child);
if (isLeft) {
nodeMap[parent].left = nodeMap[child];
} else {
nodeMap[parent].right = nodeMap[child];
}
}
return nodeMap[Object.keys(hasNoParentMap).filter(key => hasNoParentMap[key])[0]];
};
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).