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1.
请实现一个简单的事件机制，能够实现对事件的触发和监听。
如：EventEmitter.on(); EventEmitter.trigger();
const camel_hump = str => {
return str.replace(/(?:\-|\_)([a-z])/g, (input, match) => {
return match.toUpperCase();
});
}2.
使用MYSQL进行模糊查询 LIKE ‘_YOU%’,下面哪个是正确结果？
YYOUYO
_：表示任意单个字符 %：表示任意个或多个字符
3.
请求出第20个丑数。（最小因子只有2、3、5的数，称作丑数（Ugly Number）。例如6、8都是丑数，但14不是，因为它包含因子7，习惯上我们把1当做是第一个丑数）；
输入：getUglyNumber(20)
输出：36
思路:
1.按顺序将丑数保存在数组中，然后求下一个丑数；
2.下一个丑数是由数组中某个丑数A * 2，B * 3，C * 5中的最小值得来的。
3.按照题目规定，第一个丑数是1，存入数组中；
4.第二个丑数为1*2，1*3，1*5三个中的最小值；
5.第三个丑数为2*2，1*3，1*5三个中的最小值，依次类推，求出第N个数组。
const getUglyNumber = n => {
if (n >= 1) {
const temp = [1],
result = [1];
let i = 1,
index2 = 0,
index3 = 0,
index5 = 0;
while (result.length < n) {
temp[i] = Math.min(temp[index2] * 2, temp[index3] * 3, temp[index5] * 5);
if (temp[i] == temp[index2] * 2) {
index2++;
} else if (temp[i] == temp[index3] * 3) {
index3++;
} else if (temp[i] == temp[index5] * 5) {
index5++;
}
if (result.indexOf(temp[i]) == -1) {
result.push(temp[i]);
}
i++;
}
return result[n - 1];
}
}4.
请判断一个字符串出现次数最多的字符及出现次数？
输入：const str = 'asddfgdfwwqeweqwezczxcsdfgdgd';
输出：’d’, 出现6次
const str = 'asddfgdfwwqeweqwezczxcsdfgdgd';
let map = {};
let maxTimes = 0,
target;
for (let i = 0; i < str.length;i++) {
if (map[str[i]] !== undefined) {
map[str[i]]++;
} else {
map[str[i]] = 1;
}
if (map[str[i]] > maxTimes) {
maxTimes = map[str[i]];
target = str[i];
}
}
map = null;5.
求字符串 'hello world' 对应的ASCII码数组，并按照编码大小逆序。
输入：'hello world’
输出：[119, 114, 111, 111, 108, 108, 108, 104, 101, 100, 32]
var str = 'hello world';
var arr=[];
for(var i=0;i<str.length;i++){
arr.push(str[i].charCodeAt());
}
arr.sort((a,b)=>a-b).reverse();
console.log(arr);十进制ASCII码转换成字符：String.fromCharCode(num1[, ...[, numN]])
String.fromCodePoint(65) // A
String.fromCodePoint(90) // Z
String.fromCodePoint(97) // a
String.fromCodePoint(122) // z字符转换成十进制ASCII码：'a'.charCodeAt()
'A'.charCodeAt() // 65
'a'.charCodeAt() // 97
'Z'.charCodeAt() // 90
'z'.charCodeAt() // 1226.调用函数无返回值，要求改变原有数组
输入描述： ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"]
输出描述：["b","l","u","e"," ","i","s"," ","s","k","y"," ","t","h","e"]
var reverseWords = function(s) {
var arr=[];
for(var i=s.length-1;i>=0;i--){
if(s[i]===' ') arr= arr.concat(s.splice(i,s.length-1));
}
arr.shift();
arr.push(" ");
for(var i=arr.length-1;i>=0;i--){
s.unshift(arr[i]);
}
console.log(s);
console.log(arr);
};
// JSON.stringify
var s = ["t","h","e"," ","s","k","y"," ","i","s"," ","b","l","u","e"];
// s = JSON.parse(s);
reverseWords(s);
var quotedAndCommaSeparated = '["' + s.join('","') + '"]';
console.log(quotedAndCommaSeparated);