js中字符和数组一些基本算法题

function reverseString(str) {
  str = str.split(‘‘).reverse().join(‘‘);
 
  return str;
}

reverseString("hello");

function palindrome(str) {
  // Good luck!
  
  str=str.replace(/[\ |\~|\`|\!|\@|\#|\$|\%|\^|\&|\*|\(|\)|\-|\_|\+|\=|\||\\|\[|\]|\{|\}|\;|\:|\"|\‘|\,|\<|\.|\>|\/|\?]/g,"");  //去除标点符号,这是我百度的，js的正则不是很熟悉
  str = str.replace(/\s+/g);
  str = str.toLowerCase();
  var arr = str.split(‘‘);
      arr = arr.reverse();
   var str1 = arr.join("");
  if(str === str1){
  return true;}
  return false;
}



palindrome("eye");

/*

palindrome("eye") 应该返回一个布尔值
palindrome("eye") 应该返回 true.
palindrome("race car") 应该返回 true.
palindrome("not a palindrome") 应该返回 false.
palindrome("A man, a plan, a canal. Panama") 应该返回 true.
palindrome("never odd or even") 应该返回 true.
palindrome("nope") 应该返回 false.
palindrome("almostomla") 应该返回 false.
palindrome("My age is 0, 0 si ega ym.") 应该返回 true.
palindrome("1 eye for of 1 eye.") 应该返回 false.
palindrome("0_0 (: /-\ :) 0-0") 应该返回 true.



*/

/*这题很简单，主要是要明白  split() 是把字符串分割成数组 
join() 是把 数组变成字符串  
toLowerCase() toUpperCase() 大小写转换，注意，只对字母有效，其他字符（eg:/,!@）无效
*/

function titleCase(str) {
 str = str.split(" ");//按照空格把字符串分割成数组
    for (var i = 0; i < str.length; i++) {
        str[i] = str[i].toLowerCase();
        str[i] = str[i].substring(0, 1).toUpperCase() + str[i].substring(1);
    }
    return str.join(" ");//通过空格把数组连接成字符串
}

titleCase("I‘m a little tea pot");

function confirmEnding(str, target) {
  // "Never give up and good luck will find you."
  // -- Falcor
  
  return str.substr(str.length-target.length) == target ? true:false;
}

confirmEnding("Bastian", "n");
confirmEnding("He has to give me a new name", "na");
/*
confirmEnding("Bastian", "n") 应该返回 true.
confirmEnding("Connor", "n") 应该返回 false.
confirmEnding("Walking on water and developing software from a specification are easy if both are frozen", "specification") 应该返回 false.
confirmEnding("He has to give me a new name", "name") 应该返回 true.
confirmEnding("He has to give me a new name", "me") 应该返回 true.
confirmEnding("He has to give me a new name", "na") 应该返回 false.
confirmEnding("If you want to save our world, you must hurry. We dont know how much longer we can withstand the nothing", "mountain") 应该返回 false.
*/

function repeat(str, num) {
  // repeat after me
  var newstr = str;
  if(num >1){
    for(var i = 1; i< num ; i ++){
      str +=newstr;
    }
    return str;
  }else if(num == 1){
    return str;
  }else{
    return "";
  }
  
}

repeat("abc", 3);
repeat("*", 3);

 1 function chunk(arr, size) {
 2   // Break it up.
 3 var arr1 = [];
 4     for (var i = 0; i < arr.length; i = i + size) {
 5         var arr2 = arr;
 6         arr1.push(arr2.slice(i, i + size));
 7     }
 8     return arr1;
 9 }
10 
11 chunk(["a", "b", "c", "d"], 2);