1. Level traversal of binary tree

• Create a binary tree

class Binary{
  constructor(data,left,right){
  this.data = data
  this.left = left
  this.right = right
 }
}

• Output function

function Output(){
  const left = new Binary(1, new Binary(2),new Binary(3))
  const right = new Binary(4,new Binary(5),new Binary(6))
  const root = new Binary(0,left,right)
//console.log(root) 
/*
       0
     /  \
    1    4
   / \  / \
  2  3  5  6
 */

 inOrder(root) // 2 1 3 0 5 4 6
 preOrder(root) //0 1 2 3 4 5 6
 postOrder(root) //2,3,1,5,6,4,0
 levelOrder(root) // 0,1,4,2,3,5,6
}()

• First access the left subtree, then access itself, then access the right subtree

function inOrder(root){
 if(root){
   inOrder(root.left)
   console.log(root.data)
   inOrder(root.right)
 }
}

• Access itself first, then the left subtree, then the right subtree

function preOrder(root){
 if(root){
  console.log(root.data)
  preOrder(root.left)
  preOrder(root.right)
 }
}

• First access the left subtree, then access the right subtree and then access itself

function postOrder(root){
 if(root){
   postOrder(root.left)
   postOrder(root.right)
   console.log(root.data)
 }
}

• Hierarchy traversal

function levelOrder(root){
   var queue = []
   queue.unshift(root)
   while(queue.length){
     var current = queue.pop()
     console.log(current.data)
     if(current.left){
       queue.unshift(current.left)
     }
     if(current.right){
       queue.unshift(current.right)
     }
   }
}

2. Hierarchical traversal of multi tree

• Create a multi fork tree

class TreeNode {
  constructor(data){
    this.data = data
    this.children = []
  }
}

• Output function

function main(){
 const root = new TreeNode(0)
 const node2 = new TreeNode(2)
 cosnt node2.children.push(new TreeNode(7))
 const node2.chilfren.push(new TreeNode(8))
 const node2.children.push(new TreeNode(9))
 const node4 = new TreeNode(4)
 const node3 = new TreeNode(3)
 const node3.children.push(new TreeNode(6))
 const node3.children.push(new TreeNode(5))
 root.children.push(node2)
 root.children.push(node4)
 root.children.push(node3)
//console.log(root)
/*
                        0
                   /    |    \
                  2     4     3
               /  |  \       /  \
              7   8   9     6    5  
*/
traverse1(root)
traverse2(traverse2[root])
var result = []
traverse3([root],result)
console.log(result)
levelOrder(root)
}()

Recursively traversing each node

• Method 1

function traverse1(node){
 if(!node){
  return []
 }
var result = []
result.push(node.data)
if(node.children){
for(var i = 0;i<=node.children.length-1;i++){
  result = result.concat(traverse1(node.children[i]))
}
 return result
}
}

• Method 2

function tranverse2(nodeList){
if(!nodeList){
return []
}
var result = []
for(var i=0;i<=nodeList.length-1;i++){
 result.push(nodeList[i].data)
  if(nodeList[i].children){
    result = result.concat(traverse2(nodeList[i].children))
  }
 }
return result
}

• Method 3

function traverse3(nodeList,result){
  if(!nodeList){
    return false
  }
 for(var i=0;i<=nodeList.length-1;i++){
  resule.push(nodeList[i].data)
  if(nodeList[i].childern){
    traverse3(nodeList[i].children,result)
  }
 }
}

Traverse each node hierarchically

funciton levelOrder(root){
 var queue = []
 queue.unshift(root)
var result = []
while(quue.length){
 var current  = queue.pop()
 result.push(current.data)
 for(var i =0;i<=current.children.length-1;i++){
   if(current.children[i]){
    queue.unshift(current.children[i])
    }
  }
 }
console.log(result)
}