常見的js算法面試題收集，es6實現

一、js 統計一個字符串出現頻率最高的字母/數字

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
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二、數組去重

2.一、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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2.二、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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2.三、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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2.四、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']
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三、翻轉字符串

let str ="Hello Dog";
const reverseString = str =>{
    return [...str].reverse().join("");
}
console.log(reverseString(str))   // goD olleH
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四、數組中最大差值

4.一、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
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4.二、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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五、不借助臨時變量，進行兩個整數的交換

5.一、數組解構

let a = 2,
    b = 3;
    [b,a] = [a,b]
    console.log(a,b)   // 3 2
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5.二、算術運算（加減）

輸入a = 2,b = 3,輸出 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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5.三、邏輯運算（異或）

let a = 2,
    b = 3;
const swop = (a, b) => {
    a ^= b; //x先存x和y二者的信息
    b ^= a; //保持x不變，利用x異或反轉y的原始值使其等於x的原始值
    a ^= b; //保持y不變，利用x異或反轉y的原始值使其等於y的原始值
    return [a,b];
}
console.log(swop(2,3)) // [3,2]
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六、排序 (從小到大)

6.一、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]
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結語

持續更新，持續更新...

錯漏之處，敬請斧正

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