前端常见算法JS实现「建议收藏」

//冒泡排序
function bubbleSort(arr){
    var i = j = 0;
    for(i=1;i<arr.length;i++){
        for(j=0;j<=arr.length-i;j++){
            var temp = 0;
            if(arr[j]>arr[j+1]){
                temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
            }
        }
    }
}

//快速排序
function quickSort(arr,l,r){
    if(l < r){
        var i = l, j = r, x = arr[i];
        while(i<j){
            while(i<j && arr[j]>x)
                j--;
            
            if(i<j)
                //这里用i++，被换过来的必然比x小，赋值后直接让i自加，不用再比较，可以提高效率
                arr[i++] = arr[j];
            
            while(i<j && arr[i]<x)
                i++;
            
            if(i<j)
                //这里用j--，被换过来的必然比x大，赋值后直接让j自减，不用再比较，可以提高效率
                arr[j--] = arr[i];
        }
        arr[i] = x;
        
        quickSort(arr, l, i-1);
        quickSort(arr, i+1, r);
    }
}

function merge(left, right) {
    var result = [],
        il = 0,
        ir = 0;

    while (il < left.length && ir < right.length) {
        if (left[il] < right[ir]) {
            result.push(left[il++]);
        } else {
            result.push(right[ir++]);
        }
    }
    while(left[il]){
        result.push(left[il++]);
    }
    while(right[ir]){
        result.push(right[ir++]);
    }
    return result;
}

function palindrome(str){
    // \W匹配任何非单词字符。等价于“[^A-Za-z0-9_]”。
    var re = /[\W_]/g;
    // 将字符串变成小写字符,并干掉除字母数字外的字符
    var lowRegStr = str.toLowerCase().replace(re,'');
    // 如果字符串lowRegStr的length长度为0时，字符串即是palindrome
    if(lowRegStr.length===0)
        return true;
    // 如果字符串的第一个和最后一个字符不相同，那么字符串就不是palindrome
    if(lowRegStr[0]!=lowRegStr[lowRegStr.length-1])
        return false;
    //递归
    return palindrome(lowRegStr.slice(1,lowRegStr.length-1));
}

function reverseString(str){
    var tmp = '';
    for(var i=str.length-1;i>=0;i--)
        tmp += str[i];
    return tmp
}

function reverseString2(str){
    var arr = str.split("");
    var i = 0,j = arr.length-1;
    while(i<j){
        tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
        i++;
        j--;
    }
    return arr.join("");
}

function randomString(n){
    var str = 'abcdefghijklmnopqrstuvwxyz0123456789';
    var tmp = '';
    for(var i=0;i<n;i++)
        tmp += str.charAt(Math.round(Math.random()*str.length));
    return tmp;
}

function findMaxDuplicateChar(str) {
    if(str.length == 1) {
        return str;
    }
    var charObj = {};
    for(var i = 0; i < str.length; i++) {
        if(!charObj[str.charAt(i)]) {
            charObj[str.charAt(i)] = 1;
        } else {
            charObj[str.charAt(i)] += 1;
        }
    }
    var maxChar = '',
        maxValue = 1;
    for(var k in charObj) {
        if(charObj[k] >= maxValue) {
            maxChar = k;
            maxValue = charObj[k];
        }
    }
    return maxChar + '：' + maxValue;
}

function unique(arr){
    var obj = {}
    var data = []
    for(var i in arr){
        if(!obj[arr[i]]){
            obj[arr[i]] = true;
            data.push(arr[i]);
        }
    }
    return data;
}

function getMaxProfit(arr){
    var min = arr[0], max = arr[0];
    for(var i=0;i<arr.length;i++){
        if(arr[i]<min)
            min = arr[i];
        if(arr[i]>max)
            max = arr[i];
    }
    return max - min;
}

//1. 非递归实现
function factorialize(num) {
    var result = 1;
    if(num < 0) return -1;
    if(num == 0 || num == 1) return 1;
    while(num>1)
        result *= num--;
    return result;
}
//2. 递归实现
function factorialize(num) {
    var result = 1;
    if(num < 0) return -1;
    if(num == 0 || num == 1) return 1;
    if(num > 1){
        return num*factorialize(num-1);
    }
}

function getfib(n){
    if(n == 0)
        return 0;
    if(n == 1)
        return 1;
    if(n > 1){
        return getfib(n-1) + getfib(n-2);
    }
}
function fibo(len){
    var fibo = [];
    for(var i=0;i<len;i++)
        fibo.push(getfib(i));
    return fibo;
}

function getFibonacci(n) {
    var fibarr = [];
    var i = 0;
    while(i < n) {
        if(i <= 1) {
            fibarr.push(i);
        } else {
            fibarr.push(fibarr[i - 1] + fibarr[i - 2])
        }
        i++;
    }
    return fibarr;
}

function binary_search(arr, key) {
    var low = 0,
        high = arr.length - 1;
    while(low <= high){
        var mid = parseInt((high + low) / 2);
        if(key == arr[mid]){
            return  mid;
        }else if(key > arr[mid]){
            low = mid + 1;
        }else if(key < arr[mid]){
            high = mid -1;
        }
    }
    return -1;
};

function binary_search2(arr, low, high, key) {
    if(low > high)
        return -1;
    var mid = parseInt((low + high)/2);
    if(key == arr[mid])
        return mid;
    else if(key > arr[mid])
        return binary_search2(arr, mid+1, high, key);
    else if(key < arr[mid])
        return binary_search2(arr, low, mid-1, key);
}