(编辑：jimmy 日期: 2024/12/23 浏览：2)
本文基于Free Code Camp基本算法脚本“查找字符串中最长的单词”。
在此算法中，我们要查看每个单词并计算每个单词中有多少个字母。然后，比较计数以确定哪个单词的字符最多，并返回最长单词的长度。
在本文中，我将解释三种方法。首先使用FOR循环，其次使用sort（）方法，第三次使用reduce（）方法。
算法挑战
提供的测试用例
function findLongestWord(str) {
return str.length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");
1.使用FOR循环查找最长的单词
对于此解决方案，我们将使用String.prototype.split（）方法
我们将需要在split（）方法的括号之间添加一个空格
var strSplit = “The quick brown fox jumped over the lazy dog”.split(‘ ‘);
它将输出一个由单词组成的数组：
var strSplit = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”];
如果不在括号中添加空格，则将得到以下输出：
var strSplit = [“T”, “h”, “e”, “ “, “q”, “u”, “i”, “c”, “k”, “ “, “b”, “r”, “o”, “w”, “n”, “ “, “f”, “o”, “x”, “ “, “j”, “u”, “m”, “p”, “e”, “d”, “ “, “o”, “v”, “e”, “r”, “ “, “t”, “h”, “e”, “ “, “l”, “a”, “z”, “y”, “ “, “d”, “o”, “g”];
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Initiate a variable that will hold the length of the longest word
var longestWord = 0;
// Step 3. Create the FOR loop
for(var i = 0; i < strSplit.length; i++){
if(strSplit[i].length > longestWord){ // If strSplit[i].length is greater than the word it is compared with...
longestWord = strSplit[i].length; // ...then longestWord takes this new value
}
}
/* Here strSplit.length = 9
For each iteration: i = "The".length > 0)"quick".length > 3)"brown".length > 5)"fox".length > 5)"jumped".length > 5)"over".length > 6)"the".length > 6)"lazy".length > 6)"dog".length > 6)"The quick brown fox jumped over the lazy dog");
没有注释：
function findLongestWord(str) {
var strSplit = str.split(' ');
var longestWord = 0;
for(var i = 0; i < strSplit.length; i++){
if(strSplit[i].length > longestWord){
longestWord = strSplit[i].length;
}
}
return longestWord;
}
findLongestWord("The quick brown fox jumped over the lazy dog");
2.使用sort（）方法找到最长的单词
对于此解决方案，我们将使用Array.prototype.sort（）方法按照某种排序标准对数组进行排序，然后返回此数组的第一个元素的长度。
就我们而言，如果我们只是对数组排序
var sortArray = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”].sort();
我们将得到以下输出：
var sortArray = [“The”, “brown”, “dog”, “fox”, “jumped”, “lazy”, “over”, “quick”, “the”];
在Unicode中，数字在大写字母之前，而在小写字母之前。
我们需要按照某种排序标准对元素进行排序
[].sort(function(firstElement, secondElement) { return secondElement.length — firstElement.length; })
比较第二个元素的长度和数组中第一个元素的长度。
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Sort the elements in the array
var longestWord = strSplit.sort(function(a, b) {
return b.length - a.length;
});
/* Sorting process
a b b.length a.length var longestWord
"The" "quick" 5 3 ["quick", "The"]
"quick" "brown" 5 5 ["quick", "brown", "The"]
"brown" "fox" 3 5 ["quick", "brown", "The", "fox"]
"fox" "jumped" 6 3 ["jumped", quick", "brown", "The", "fox"]
"jumped" "over" 4 6 ["jumped", quick", "brown", "over", "The", "fox"]
"over" "the" 3 4 ["jumped", quick", "brown", "over", "The", "fox", "the"]
"the" "lazy" 4 3 ["jumped", quick", "brown", "over", "lazy", "The", "fox", "the"]
"lazy" "dog" 3 4 ["jumped", quick", "brown", "over", "lazy", "The", "fox", "the", "dog"]
*/
// Step 3. Return the length of the first element of the array
return longestWord[0].length; // var longestWord = ["jumped", "quick", "brown", "over", "lazy", "The", "fox", "the", "dog"];
// longestWord[0]="jumped" => jumped".length => 6
}
findLongestWord("The quick brown fox jumped over the lazy dog");
没有注释：
function findLongestWord(str) {
var longestWord = str.split(' ').sort(function(a, b) { return b.length - a.length; });
return longestWord[0].length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");
3.使用reduce（）方法找到最长的单词
对于此解决方案，我们将使用Array.prototype.reduce（）。
reduce（）对数组中存在的每个元素执行一次回调函数。
您可以提供一个初始值作为要减少的第二个参数，这里我们将添加一个空字符串“”。
[].reduce(function(previousValue, currentValue) {...}, “”);
function findLongestWord(str) {
// Step 1. Split the string into an array of strings
var strSplit = str.split(' ');
// var strSplit = "The quick brown fox jumped over the lazy dog".split(' ');
// var strSplit = ["The", "quick", "brown", "fox", "jumped", "over", "the", "lazy", "dog"];
// Step 2. Use the reduce method
var longestWord = strSplit.reduce(function(longest, currentWord) {
if(currentWord.length > longest.length)
return currentWord;
else
return longest;
}, "");
/* Reduce process
currentWord longest currentWord.length longest.length if(currentWord.length > longest.length)"The" "" 3 0 yes "The"
"quick" "The" 5 3 yes "quick"
"brown" "quick" 5 5 no "quick"
"fox" "quick" 3 5 no "quick"
"jumped" "quick" 6 5 yes "jumped"
"over" "jumped" 4 6 no "jumped"
"the" "jumped" 3 6 no "jumped"
"lazy" "jumped" 4 6 no "jumped"
"dog" "jumped" 3 6 no "jumped"
*/
// Step 3. Return the length of the longestWord
return longestWord.length; // var longestWord = "jumped"
// longestWord.length => "jumped".length => 6
}
findLongestWord("The quick brown fox jumped over the lazy dog");
没有注释：
function findLongestWord(str) {
var longestWord = str.split(' ').reduce(function(longest, currentWord) {
return currentWord.length > longest.length "");
return longestWord.length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");