JavaScript

solution on Find the longest wor

2017-12-05  本文已影响15人  XERO75

solution on Find the longest word and return its length

找出字符串(可能是一句话)中最长的单词并且将其长度输出。这个算法其实就是让我们看看字符串中有多少个词,每个词有多少个字母,然后对这些词进行比较,找出字母数最多的那个词,并且返回这个最长字符数单词的长度。

步骤分析

JavaScript方法

在写findLongestWord(str)函数实现文章开头所述的功能,根据上面的实现思路,讲大致会用到下面有关于JavaScript点:

其中 String.prototype.split() 主要是用来将字符串str转换成数组arr。比如:

"May the force be with you".split(" ")
//["May","the","force","be","with","you"]

这里需要注意,在使用split()方法时,""中间的要有一个空格(" ")。否则将会转变成这样一个数组:

"May the force be with you".split(""); 
// ["M", "a", "y", " ", "t", "h", "e", " ", "f", "o", "r", "c", "e", " ", "b", "e", " ", "w", "i", "t", "h", " ", "y", "o", "u"]

Math.max()方法可以很简单的从一个数组中取出最大的那个值

Array.prototype.max = function(){
  return Math.max.apply({},this);
}
var arr=[1,45,23,,3,6,3,4,564,45];
arr.max();//564

测试用例

通过测试用例是最好的检测方法,检测自己写的函数是否符合要求,下面提供几个测试用例:

实现方法

for循环

function findLongestWord(str) { 
// 第1步:将传给str的值"May the force be with you"转换成数组 
var array = str.split(' '); 
// 得到数组 ["May", "the", "force", "be", "with", "you"] 
var longest = 0; 
// 第2步:对数组array做遍历,并且将符合条件的值赋值给longest 
for (var i = 0; i < array.length; i++) { 
// array.length = 6 

if (array[i].length > longest) { 
// 如果为true,longest值为array[i].length; 
longest = array[i].length;
 } 
 }
  /* * array = ["May", "the", "force", "be", "with", "you"] 
  * array.length = 6 * 
  * 遍历次数 i = ? i < array.length i++ array[i].length longest array[i].length > longest longest= array[i].length 
  * 1st 0 yes 1 "May".length=3 0 3 > 0 => yes 3 
  * 2nd 1 yes 2 "the".length=3 3 3 > 3 => no 3 
  * 3rd 2 yes 3 "force".length=5 3 5 > 3 => yes 5 
  * 4th 3 yes 4 "be".length=2 5 2 > 5 => no 5 
  * 5th 4 yes 5 "with".length=4 5 4 > 5 => no 5 
  * 6th 5 yes 6 "you".length=3 5 3 > 5 => no 5 
  * 7th 6 no * End Loop */ 
  * // 第3步:输出最长词的长度 
  * return longest; // 5 }

你可以把前面的测试示例都运行一回,看看是否得到的值是正确的,如果不是,那就要检查一下代码是不是哪里出错了。除了上述的方法之外,还可以for循环之后,通过Math.max()直接将数组arrNum中的最大值取出。如下所示:

function findLongestWord(str){
// 1st:将传给str的值为:"May the force be with you"转成数组

// 得到数组arr=["May","the","force","be","with","you"]
var arrNum[];

// 2st:对数组arr做遍历
for(var i=o; i<arr.length; i++){
// 讲数组arr中每个元素的长度length放到一个新数组arrNum中
arrNum.push(arr[i].length);

    /* 
     * 遍历次数 i = ? i < arr.length i++ arr[i] arr[i].length arrNum 
     * 1st 0 yes 1 "May" 3 [3] 
     * 2nd 1 yes 2 "the" 3 [3,3] 
     * 3rd 2 yes 3 "force" 5 [3,3,5] 
     * 4th 3 yes 4 "be" 2 [3,3,5,2] 
     * 5th 4 yes 5 "with" 4 [3,3,5,2,4]      * 6th 5 yes 6 "you" 3 [3,3,5,2,4,3] 
     * 7th 6 no * End Loop 
     */
 }      
 
 // 3st:通过Math.max()取出数组arrNum中最大值,并且输出
 return Math.max.apply(null,arrNum);//5
 }

sort()方法

function findLongestWord(str){
// 1st:将传给str的值为:"May the force be with you"转成数组
var strArr=str.split(" ");
//得到数组arr=["May","the","force","be","with","you"]
var numArr=[];
var sortArr=[];

// 2st: 对strArr数组做遍历,并把数组中每个词的length放到新数组numArr中
for(var i=0; i<strArr.length; i++){
numArr[i]=strArr[i].length;
}
// 新数组:numArr=[3,3,5,2,4,3]

// 3st: 使用sort()对数组numArr排序,有小到大
sortArr=numArr.sort(funtion compare(a,b){
return a-b;
});
// 排序后的数组:sortArr=[2,3,3,3,4,5]

// 4st: 通过pop()取到数组sortArr中最后一个值,赋值给longestWord
var longestWord=sortArr.pop();//5

// 5st: 输出longestWord
return longestWord;//5
}

或者

function findLongestWord(str) { 
// 第1步:将传给str的值为:"May the force be with you"转成数组 
var arr = str.split(' '); 
// 得到数组 arr = ["May", "the", "force", "be", "with", "you"] 
// 第2步: 通过sort()将数组arr按由小到大排序 
arr = arr.sort(function(a, b) { 
return a.length - b.length; 
}); 
    /* 
    * a b b.length a.length arr 
    * "May" "the" 3 3 ["May","the"] 
    * "the" "force" 5 3 ["May","the","force"] 
    * "force" "be" 2 5 ["be","May","the","force"] 
    * "be" "with" 4 2 ["be","May","the","with","force"] 
    * "with" "you" 3 4 ["be","May","the","you","with","force"] 
    */ 
// 最长的字符排在数组最后 
// 第3步:获取数组最长字符的长度 
var longestString = arr.pop().length; // 5 
// 第4步:返回最长字符的长度 return longestString; // 5 }

reduce()方法
function findLongestWord(str){
// 1st: 将传给str的值为:"May the force be with you"转成数组
var strSplit=str.split(' ');

//得到数组 arr = ["May", "the", "force", "be", "with", "you"];

// 2st: 使用reduce方法,取得strSplit数组中最长的元素
var longestWord = strSplit.reduce(function(longest,currentWord){
return currentWord.length > longestWord ? current : longest;},"");

// 取到最长的元素longestWord = "force" 
/* 
 * strSplit = ["May", "the", "force", "be", "with", "you"]; 
 * currentWord longest currentWord.length longest.length currentWord.length > longest.length longestWord 
 * "May" "" 3 0 yes "May" 
 * "the" "May" 3 3 no "May" 
 * "force" "May" 5 3 yes "force" 
 * "be" "force" 2 5 no "force" 
 * "with" "force" 4 5 no "force" 
 * "you" "force" 3 5 no "force" 
 */ 
 
 // 第3步. 返回longestWord的length
 return longestWord.length;//5
 // longestWord.length => "force".length =>5
 }

也可以使用reduce()方法和Math.max()方法配合使用:
function findLongestWord(str){
// 1st: 将传给str的值为:"May the force be with you"转成数组
var strSplit = str.split(' ');
// 得到数组strSplit = ["May", "the", "force", "be", "with", "you"];

// 2st: 使用reduce方法,取到strSplit数组中最长的元素length,并且返回
return strSplit.reduce(function(longest,currentWord){
return Math.max(longest, cunrrentWord.length),0);// "force".length => 5
}

总结

文章中通过几种不同的方法实现了:找出字符串(可能是一句话)中最长的单词并且将其长度输出。主要使用了for、sort()和reduce()方法,当然在具体实现功能过程中,还运用到了JavaScript中的split()、pop()和Math.max()等方法。

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