常见的js算法面试题收集，es6实现

19,297 阅读2分钟

1、js 统计一个字符串出现频率最高的字母/数字

``````let str = 'asdfghjklaqwertyuiopiaia';
const strChar = str => {
let string = [...str],
maxValue = '',
obj = {},
max = 0;
string.forEach(value => {
obj[value] = obj[value] == undefined ? 1 : obj[value] + 1
if (obj[value] > max) {
max = obj[value]
maxValue = value
}
})
return maxValue;
}
console.log(strChar(str))    // a
``````

2、数组去重

2.1、forEach
``````let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
let obj = {}
arr.forEach(value => {
obj[value] = 0
})
return Object.keys(obj)
}
console.log(unique(arr))  // ['1','2','3','a','b']
``````
2.2、filter
``````let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
return arr.filter((ele, index, array) => {
return index === array.indexOf(ele)
})
}
console.log(unique(arr))  // ['1','2','3','a','b']
``````
2.3、set
``````let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
return [...new Set(arr)]
}
console.log(unique(arr))  // ['1','2','3','a','b']
``````
2.4、reduce
``````let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr.reduce((map, item) => {
map[item] = 0
return map
}, {})
console.log(Object.keys(unique))  // ['1','2','3','a','b']
``````

3、翻转字符串

``````let str ="Hello Dog";
const reverseString = str =>{
return [...str].reverse().join("");
}
console.log(reverseString(str))   // goD olleH
``````

4、数组中最大差值

4.1、forEach
``````let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];
const difference = arr => {
let min = arr[0],
max = 0;
arr.forEach(value => {
if (value < min) min = value
if (value > max) max = value
})
return max - min ;
}
console.log(difference(arr))  // 74
``````
4.2、max、min
``````let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];
const difference = arr => {
let max = Math.max(...arr),
min = Math.min(...arr);
return max - min ;
}
console.log(difference(arr)) // 74
``````

5、不借助临时变量，进行两个整数的交换

5.1、数组解构
``````let a = 2,
b = 3;
[b,a] = [a,b]
console.log(a,b)   // 3 2
``````
5.2、算术运算（加减）

``````let a = 2,
b = 3;
const swop = (a, b) => {
b = b - a;
a = a + b;
b = a - b;
return [a,b];
}
console.log(swop(2,3)) // [3,2]
``````
5.3、逻辑运算（异或）
``````let a = 2,
b = 3;
const swop = (a, b) => {
a ^= b; //x先存x和y两者的信息
b ^= a; //保持x不变，利用x异或反转y的原始值使其等于x的原始值
a ^= b; //保持y不变，利用x异或反转y的原始值使其等于y的原始值
return [a,b];
}
console.log(swop(2,3)) // [3,2]
``````

6、排序 (从小到大)

6.1、冒泡排序
``````let arr = [43, 32, 1, 5, 9, 22];
const sort = arr => {
arr.forEach((v, i) => {
for (let j = i + 1; j < arr.length; j++) {
if (arr[i] > arr[j]) {
[arr[i],arr[j]] = [arr[j],arr[i]]
}
}
})
return arr
}
console.log(sort(arr))  // [1, 5, 9, 22, 32, 43]
``````