js常用算法

数组去重：

function unique (arr){
  var obj={};
  var result=[];
  arr.map(()=>{
      if(!obj[item]){
          obj[item]=true;
          result.push(item)
        }
  })  
return result;
}

阶乘

function factorialize(num) {
  var result = 1;
    if(num < 0) 
      return -1;
    if(num == 0 || num == 1)
       return 1;
    while(num>1) {
      result *= num--;
    }
    return result;
}
function factorialize(num) {
  var result = 1;
  if(num < 0) 
    return -1;
  if(num == 0 || num == 1)
     return 1;
  if(num > 1)
     return num*factorialize(num-1);
}

生成菲波那切数列

function getFibonacci(n) {
  var fibarr = [];
  var i = 0;
  while(i < n) {
    if(i <= 1) {
      fibarr.push(i);
    } else {
      fibarr.push(fibarr[i - 1] + fibarr[i - 2])
    }
    i++;
  }
  return fibarr;
}

let count = 0;
function fn(n) {
    let cache = {};
    function _fn(n) {
        if (cache[n]) {
            return cache[n];
        }
        count++;
        if (n == 1 || n == 2) {
            return 1;
        }
        let prev = _fn(n - 1);
        cache[n - 1] = prev;
        let next = _fn(n - 2);
        cache[n - 2] = next;
        return prev + next;
    }
    return _fn(n);
}

二分查找

function binary_search(arr, key) {
  var low = 0,
      high = arr.length - 1;
  while(low <= high){
    var mid = parseInt((high + low) / 2);
    if(key == arr[mid]){
      return mid;
    }else if(key > arr[mid]){
      low = mid + 1;
    }else if(key < arr[mid]){
      high = mid -1;
    }
  }
  return -1;
}

实现栈的功能

定义一个栈

function Stack () {
    this.dataStore = [];    //初始化为空
    this.top = 0;           //记录栈顶位置
}

实现栈的pop,push

//元素入栈，栈顶位置加1
function push( ele ){
    this.dataStore[this.top++] = ele;
}
//元素出栈，栈顶-1
function pop(){
    return this.dataStore[--this.top];
}

实现链表的find，remove，add功能

定义一个链表

function Node(ele) {
    this.element = ele;   //当前节点的元素
    this.next = null;         //下一个节点链接
}

查找元素

function find ( item ) {
    var currNode = this.head;
    while ( currNode.element != item ){
        currNode = currNode.next;
    }
    return currNode;
}

插入元素

function insert ( new , item ) {
    var newNode = new Node( new );
    var currNode = this.find( item );
    newNode.next = currNode.next;
    currNode.next = newNode;
}

删除元素

//找到删除元素的前一个节点
function findPrev( item ) {
    var currNode = this.head;
    while ( !( currNode.next == null) && ( currNode.next.element != item )){
        currNode = currNode.next;
    }
    return currNode;
}

function remove ( item ) {
    var prevNode = this.findPrev( item );
    if( !( prevNode.next == null ) ){
        prevNode.next = prevNode.next.next;
    }
}

实现队列的in，out

定义队列

function Queue(){
var this.queue=[]
}

队尾in

function In(ele){
this.queue.push(ele)
}

队首out

function Out(){
this.queue.shift()
}