freeCodeCamp初级算法答案（个人做法）

1、回文

    function Stack(){
        this.dataStore=[];//数组实现的栈
        this.top=0;
        this.push=push;
        this.pop=pop;
        this.peek=peek;
        this.clear=clear;
        this.length=length;
    }
    function push(element){
        this.dataStore[this.top++]=element;
    }
    function peek(){
        return this.dataStore[this.top-1];
    }
    function pop(){
        return this.dataStore[--this.top];
    }
    function clear(){
        this.top=0;
    }
    function length(){
        return this.top;
    }
    function palindrome(str) {
        // Good luck!
        var word1="";
        var word2="";
        var stack=new Stack();
        var word=str.toLowerCase();
        word=word.replace(/\s+/g,"");
        word=word.replace(/[,]/g,"");
        word=word.replace(/[.]/g,"");
        word=word.replace(/[_]/g,"");
        word=word.replace(/[(]/g,"");
        word=word.replace(/[-]/g,"");
        word=word.replace(/[)]/g,"");
        word=word.replace(/[/]/g,"");
        word=word.replace(/[\\]/g,"");
        for(var i=0;i<word.length;i++){
            stack.push(word[i]);
        }
        while(stack.length()>0){
            word1+=stack.pop()
        }
        console.log(word);
        console.log(word1)
        if(word1===word){
            return true
        }else{
            return false
        }
    }
    console.log(palindrome("0_0 (: /-\ :) 0-0"))

2、找到最长的字符串长度/Find the Longest Word in a String

function findLongestWord(str) {
  var arryA=str.split(" ");
  var len=0;
  for(var i=0;i<arryA.length;i++){
    if(arryA[i].length>len){
      len=arryA[i].length;
    }
  }
  return len;
}

findLongestWord("The quick brown fox jumped over the lazy dog");

3、把一句话的首字母大写/Title Case a Sentence

function titleCase(str) {
        var word=str.toLowerCase();
        var arryA=word.split(" ");

        for(var i=0;i<arryA.length;i++){
            arryA[i]=arryA[i].replace(arryA[i].charAt(0),arryA[i].charAt(0).toUpperCase());
        }
        return arryA.join(" ");
    }

    console.log(titleCase("I'm a little tea pot"));

4、查找数组的最大值/Return Largest Numbers in Arrays

function largestOfFour(arr) {
        // You can do this!
        var arryA=[];
        for(var i=0;i<arr.length;i++){
            var num=0;
            for(var j=0;j<arr[i].length;j++){
                if(arr[i][j]>num){
                    num=arr[i][j];
                }
            }
            arryA.push(num);
        }
        return arryA;
    }

largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

5、验证某个字符串是否已某个字符结尾

    function confirmEnding(str, target) {
        // "Never give up and good luck will find you."
        // -- Falcor
        var len1=target.length;
        var len2=str.length;

        if(str.substr(len2-len1,len1)===target){
            return true;
        }else{
            return false;
        }
    }

  confirmEnding("Bastian", "n");

6、重复字符串

function repeatStringNumTimes(str, num) {
  // repeat after me
  var word=str;
  var string="";
  for(var i=0;i<num;i++){
      string+=word;
  }
  return string;
}

repeatStringNumTimes("abc", 3);

ES6中有String.protype.repeat()并且有支持各个浏览器的方法。

7、剪切字符串，truncateString（str,num）

function truncateString(str, num) {
  // Clear out that junk in your trunk
  var word="";
  var word1="";
  if(str.length>num&&num>3){
    word1=str.slice(0,num-3);
    word=word1+"...";
  }else if(num<=3){
      word=str.slice(0,num)+"...";
  }else if(str.length<=num){
    word=str;
  }
  return word;
}

truncateString("A-tisket a-tasket A green and yellow basket", 11);

8、按照特定规则剪切数组

chunkArrayInGroups(arr, size) 安装size的大小来剪切arr

function chunkArrayInGroups(arr, size) {
        // Break it up.
        var arrA=arr;
        var arrB=[];
        var lastArr;
        var num=arrA.length%size;
        if(num===0){
          for(var i=0;i<(arrA.length-num)/size;i++){
            arrB.push(arrA.slice(i*size,(i+1)*size));
          }
          return arrB;
        }else{
           for(var j=0;j<(arrA.length-num)/size;j++){
            arrB.push(arrA.slice(j*size,(j+1)*size));
          }
          lastArr=arrA.slice(arrA.length-num,arrA.length);
          arrB.push(lastArr);
          return arrB;
        }
    }

chunkArrayInGroups(["a", "b", "c", "d"], 2);

9、从特定位置剪切数组，返回剪切位置以后的数组/Slasher Flick

function slasher(arr, howMany) {
        // it doesn't always pay to be first
        var len=arr.length;
        var arrA=arr;
        var arrB=[];
        if(len>howMany){
            arrB=arrA.slice(howMany,len);
        }else{
            return arrB;
        }
        return arrB;
    }

slasher([1, 2, 3], 2);

10、判断一个字符串是否有另一个字符串的全部字母

function mutation(arr) {
        var word1=arr[0].toLowerCase();
        var word2=arr[1].toLowerCase();
        var message=true;
        for(var i=0;i<word2.length;i++){
            if(word1.indexOf(word2[i])<0){
                message=false;
            }
        }
        return message;
    }

mutation(["hello", "hey"]);

11、通过Array.prototype.filter()来判断数组中是否有 Falsy values（ false, null, 0, "",undefined, and NaN.）注意部分浏览器不支持

function bouncer(arr) {
        var word;
        var isFalse= function (num) {
            if(new Boolean(num).toString()){
                return num;
            };
        };
        word=arr.filter(isFalse);
        return word;
    }

bouncer([7, "ate", "", false, 9]);

12、在指定数组中去除指定元素 Array.filter()

function destroyer(arr) {
   var elemToDestroy = [];
   for(var i = 1; i < arguments.length; i++){
      elemToDestroy.push(arguments[i]);
   }
   var survived = arguments[0].filter(function(element, index){
      var toReturn = true;

      for(var i = 0; i < elemToDestroy.length; i++){
         if (element === elemToDestroy[i]){
            toReturn = false;
         }
      }
      return toReturn;
   });
   return survived;
}

console.log(destroyer([1, 2, 3, 1, 2, 3], 2, 3))

13、查找某一个数组中元素的位置

function getIndexToIns(arr, num) {
   // Find my place in this sorted array.
   var arrA=arr.sort(function(a,b){
      return a - b;
   });
   console.log(arrA)
   var index=0;
   for(var i=0;i<arrA.length;i++){
      if(arrA[i]<num){
         index=i+1;
      }else if(arrA[i]===num){
         index=i;
      }
   }
   return index;
}

getIndexToIns([40, 60], 50);

14、凯撒密码ROT-13

function rot13(str) { // LBH QVQ VG!
   return (str + '').replace(/[a-z]/gi, function (s) {
      return String.fromCharCode(s.charCodeAt(0) + (s.toLowerCase() < 'n' ? 13 : -13))
   })
}
// Change the inputs below to test
console.log(rot13("SERR PBQR PNZC"));