常见的js算法面试题收集，es6实现

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] + 1if (obj[value] > max) {max = obj[value]maxValue = value}})
return maxValue;
}
console.log(strChar(str))    // a
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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']
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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']
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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']
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2.4、reduce

let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr.reduce((map, item) => {map[item] = 0return map
}, {})
console.log(Object.keys(unique))  // ['1','2','3','a','b']
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3、翻转字符串

let str ="Hello Dog";
const reverseString = str =>{return [...str].reverse().join("");
}
console.log(reverseString(str))   // goD olleH
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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 = valueif (value > max) max = value})return max - min ;
}
console.log(difference(arr))  // 74
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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
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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
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5.2、算术运算（加减）

输入a = 2,b = 3,输出 a = 3,b = 2

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]
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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]
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6、排序 (从小到大)

6.1、冒泡排序

let arr = [43, 32, 1, 5, 9, 22];
const sort = arr => {let res = []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]
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