Given the root of an n-ary tree, return the postorder traversal of its nodes' values.
N-ary tree input serialization is represented in their level order traversal. Each group of children is separated by the null value.
Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]Input: root = [
1,null,2,3,4,5,null,null,6,7,
null,8,null,9,10,null,null,11,
null,12,null,13,null,null,14
]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]0 <= Node.val <= 10⁴- The number of nodes in the tree is in the range
[0, 10⁴]. - The height of the n-ary tree is less than or equal to
1000.
const postorder = (root) => {
if (!root) return [];
let res = [],
stack = [root];
while (stack.length > 0) {
root = stack.pop();
res.push(root.val);
for (let node of root.children) {
stack.push(node);
}
}
return res.reverse();
};I've defined a function called postorder that takes in a parameter called root. The purpose of this function is to perform a postorder traversal on a tree structure represented by the root parameter and return an array of the values of the nodes in the tree in reverse postorder.
Inside the function, there is an initial check to see if the root parameter is falsy (null or undefined). If it is, the function immediately returns an empty array.
If the root parameter is truthy, the function initializes an empty array called res to store the node values in postorder and a stack array with the root as its only element.
The function then enters a while loop that continues as long as the stack is not empty. Inside the loop, the root variable is updated by popping the last element from the stack using the pop() method. This represents the current node being processed.
The value of the current node is then pushed into the res array using the push() method. This ensures that the node values are stored in postorder.
A for loop is used to iterate over each child node of the current node. For each child node, it is pushed into the stack using the push() method. This allows for the traversal of the tree structure.
Once all the child nodes have been processed, the while loop repeats until the stack is empty. This ensures that all nodes in the tree are traversed.
Finally, the function returns the res array in reverse order using the reverse() method. This provides the node values in reverse postorder as the output of the function.
In summary, this function performs a postorder traversal on a tree structure by using a stack to keep track of the nodes. It stores the node values in postorder and returns them in reverse order as the output of the function.