javascript实现常见的算法

1. 快速排序

// 快排function quickSort(arr) {    if (arr.length < 2) {        return arr;    }    var pivIndex = Math.floor(arr.length/2);    var piv = arr.splice(pivIndex, 1)[0];    var left = [], right = [];    arr.forEach(ele => {        if (ele < piv) {            left.push(ele);        } else {            right.push(ele);        }    });    return quickSort(left).concat(piv, quickSort(right));}

2. 冒泡排序

// 简单粗暴的排序方法。每次从待排序数组中找到最小的元素放到首位function selectSort(arr) {    var tmp;    for(var i = 0; i < arr.length; i++) {        for(var j = i + 1; j < arr.length; j++) {            if (arr[j] < arr[i]) {                // 交换位置                tmp = arr[j];                arr[j] = arr[i];                arr[i] = tmp;            }        }    }    return arr;}

3. 选择排序

function selectSort(arr) {    for (var i = 0; i < arr.length - 1; i++) {        var minIndex = i, min = arr[i];        for (var j = i + 1; j < arr.length; j++) {            if (arr[j] < min) {                // 记下最小值的索引，找到待排序数组中的最小值                min = arr[j];                minIndex = j;            }        }        arr[minIndex] = arr[i];        arr[i] = min;    }    return arr;}

4. 归并排序

function _merge(left, right) {    // 归并数组    var res = [];    while(right.length && left.length) {        if (left[0] < right[0]) {            res.push(left.shift());        } else {            res.push(right.shift());        }    }    return res.concat(left, right);}function mergeSort(arr) {    if (arr.length < 2) {        return arr;    }    var pivIndex = Math.floor(arr.length/2);    return _merge(mergeSort(arr.slice(0, pivIndex)), mergeSort(arr.slice(pivIndex)));}

5. 二分查找

function halfSearch(arr, dest) {    var pivIndex = Math.floor(arr.length/2);    var piv = arr[pivIndex];    var length = arr.length;    if (length === 0) {        return null;    } else if (length === 1) {        return arr[0] === dest ? 0 : null;    } else if(piv == dest) {        return pivIndex;    } else if (piv > dest) {        // 小于目标值，向左查询        return halfSearch(arr.slice(0, pivIndex), dest);    } else {        return halfSearch(arr.slice(pivIndex+1), dest);    }}