liurubin/learn_bj

bj

learn_bj's Issues

Build tree array from flat array in javascript

function list_to_tree(list) {
  var map = {}, node, roots = [], i;
  
  for (i = 0; i < list.length; i += 1) {
    map[list[i].id] = i; // initialize the map
    list[i].children = []; // initialize the children
  }
  
  for (i = 0; i < list.length; i += 1) {
    node = list[i];
    if (node.parentId !== "0") {
      // if you have dangling branches check that map[node.parentId] exists
      list[map[node.parentId]].children.push(node);
    } else {
      roots.push(node);
    }
  }
  return roots;
}

var entries = [{
    "id": "12",
    "parentId": "0",
    "text": "Man",
    "level": "1",
    "children": null
  },
  {
    "id": "6",
    "parentId": "12",
    "text": "Boy",
    "level": "2",
    "children": null
  },
  {
    "id": "7",
    "parentId": "12",
    "text": "Other",
    "level": "2",
    "children": null
  },
  {
    "id": "9",
    "parentId": "0",
    "text": "Woman",
    "level": "1",
    "children": null
  },
  {
    "id": "11",
    "parentId": "9",
    "text": "Girl",
    "level": "2",
    "children": null
  }
];

console.log(list_to_tree(entries));

笔记

function fib(n){ 
  let arr = [1,1] 
  let i = 2
  while(i<=n){ 
    arr[i] = arr[i-1]+arr[i-2] 
    i++ 
  } 
  return arr[n]
}

let array = [
    ["Viola", "Orsino"],
    ["Orsino", "Olivia"],
    ["Olivia", "Cesario"]
];

let resultMap = array.reduce((memo,curr) => {
   memo[curr[0]] = curr[1]
   return memo
},{})


const numbers = [-1,0,2,3,4,5,6];
const doubleNumbers = numbers.reduce((acc, curr) => {
  if (curr > 0) {
  acc.push(curr * 2)
}
  return acc;
},[])

const array = ['a','b','a','c','d','c','e']
const orderedArray = array.reduce((acc, cur) => {
    acc.indexOf(cur) === -1 ? acc.push(cur) : acc
    return acc
},[])

let books = [
    {
        title: "Showings",
        author: "Julian of Norwich",
        checkouts: 45
    },
    {
        title: "The Triads",
        author: "Gregory Palamas",
        checkouts: 32
    },
    {
        title: "The Praktikos",
        author: "Evagrius Ponticus",
        checkouts: 29
    }
];

let total = books.map(function (b) { return b.checkouts })
                 .reduce(function (p, c) { return p + c} )

let flatted = [[1,2],[3,4],[4,5]].reduce((acc, cur) => acc.concat(cur), [])

const numbers = [3,4,7,8,9]
const max = numbers.reduce((acc, cur) => {
    if (cur > acc) {
        acc = cur
    }
    return acc
})

const numbers = [3,4,6,3,10,90,6,3]
const result = numbers.reduce((acc, cur) => {
    acc[cur] ? acc[cur]++ : acc[cur] = 1
    return acc
}, {})

Javascript: Find all parents for element in tree

var tree = {
  id: 1,
  children: [
  	{
		id: 3,
		parentId: 1,
		children: [
		  	{
				id: 5,
				parentId: 3,
				children: []
			}
		]
	}
  ]
}

// We will flatten it down to an object that just holds the id with the object
var lookup = {}
function mapIt (node) {
  lookup[node.id] = node;
  //recursive on all the children
  node.children && node.children.forEach(mapIt);
}
mapIt(tree)

// This takes a node and loops over the lookup hash to get all of the ancestors
function findAncestors (nodeId) {
   var ancestors = []
   var parentId = lookup[nodeId] && lookup[nodeId].parentId
   while(parentId !== undefined) {
     ancestors.unshift(parentId)
     parentId = lookup[parentId] && lookup[parentId].parentId
   }
   return ancestors;
}

// Let us see if it works
console.log("5: ",  findAncestors(5))