JS排序算法总结

冒泡排序

function bubbleSort(arr) {
    var len = arr.length;
    for (var i = 0; i < len; i++) {
        for (var j = 0; j < len - 1 - i; j++) {
            if (arr[j] > arr[j+1]) {        //相邻元素两两对比
                var temp = arr[j+1];        //元素交换
                arr[j+1] = arr[j];
                arr[j] = temp;
            }
        }
    }
    return arr;
}

选择排序

function selectionSort(arr) {
    var len = arr.length;
    var minIndex, temp;
    for (var i = 0; i < len - 1; i++) {
        minIndex = i;
        for (var j = i + 1; j < len; j++) {
            if (arr[j] < arr[minIndex]) {     //寻找最小的数
                minIndex = j;                 //将最小数的索引保存
            }
        }
        temp = arr[i];
        arr[i] = arr[minIndex];
        arr[minIndex] = temp;
    }
    return arr;
}

插入排序

function insertionSort(arr) {
    var len = arr.length;
    var preIndex, current;
    for (var i = 1; i < len; i++) {
        preIndex = i - 1;
        current = arr[i];
        while(preIndex >= 0 && arr[preIndex] > current) {
            arr[preIndex+1] = arr[preIndex];
            preIndex--;
        }
        arr[preIndex+1] = current;
    }
    return arr;
}

希尔排序

希尔排序是插入排序的一种更高效率的实现。它与插入排序的不同之处在于，它会优先比较距离较远的元素。希尔排序的核心在于间隔序列的设定。

function shellSort(arr) {
    var len = arr.length,
        temp,
        gap = 1;
    while(gap < len/3) {          //动态定义间隔序列
        gap =gap*3+1;
    }
    for (gap; gap > 0; gap = Math.floor(gap/3)) {
        for (var i = gap; i < len; i++) {
            temp = arr[i];
            for (var j = i-gap; j >= 0 && arr[j] > temp; j-=gap) {
                arr[j+gap] = arr[j];
            }
            arr[j+gap] = temp;
        }
    }
    return arr;
}

归并排序

function mergeSort(arr) {  //采用自上而下的递归方法
    var len = arr.length;
    if(len < 2) {
        return arr;
    }
    var middle = Math.floor(len / 2),
        left = arr.slice(0, middle),
        right = arr.slice(middle);
    return merge(mergeSort(left), mergeSort(right));
}

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

    while (left.length && right.length) {
        if (left[0] <= right[0]) {
            result.push(left.shift());
        } else {
            result.push(right.shift());
        }
    }

    while (left.length)
        result.push(left.shift());

    while (right.length)
        result.push(right.shift());

    return result;
}

快速排序

方法1：

const quickSort = function (array) {
    if (array.length <= 1) {
        return array;
    }
    const pivotIndex = parseInt(array.length / 2);
    const pivot = Number(array.splice(pivotIndex, 1));
    const left = [];    const right = [];
    for (let i = 0; i < array.length; i++) {
        if (array[i] < pivot) {
            left.push(array[i]);
        } else {
            right.push(array[i]);
        }
    }
    return quickSort(left).concat([pivot], quickSort(right));
};

方法2：

function quickSort(array, left, right) {
    if (left < right) {
        let x = array[right], i = left - 1;
        for (let j = left; j <= right; j++) {
            if (array[j] <= x) {
                i++;
                const temp = array[i];
                array[i] = array[j];
                array[j] = temp;
            }
        }
        quickSort(array, left, i - 1);
        quickSort(array, i + 1, right);
    }
    return array;
}
// left = 0; right = array.length-1

堆排序

function heapSort(array) {
    let length = array.length;
    for (let i = parseInt(array.length / 2) - 1; i >= 0; i--) {
        heap(array, i, length);
    }
    for (let j = length - 1; j >= 1; j--) {
        const temp = array[0];
        array[0] = array[j];
        array[j] = temp;
        heap(array, 0, --length);
    }
    return array;
}
function heap(array, x, length) {
    let l = 2 * x + 1, r = 2 * x + 2, largest = x;
    if (l < length && array[l] > array[largest]) {
        largest = l;
    }
    if (r < length && array[r] > array[largest]) {
        largest = r;
    }
    if (largest != x) {
        const temp = array[x];
        array[x] = array[largest];
        array[largest] = temp;
        heap(array, largest, length);
    }
}

计数排序

function countSort(array) {
    const newArray = [], C = [];
    let min = array[0];
    let max = array[0];
    for (let i = 0; i < array.length; i++) {
        if (min >= array[i]) {
            min = array[i];
        }
        if (max <= array[i]) {
            max = array[i];
        }
        if (C[array[i]] = C[array[i]]) {
            C[array[i]]++;
        } else {
            C[array[i]] = 1;
        }
    }
    for (let j = min; j < max; j++) {
        C[j + 1] = (C[j + 1] || 0) + (C[j] || 0);
    }
    for (let k = array.length - 1; k >= 0; k--) {
        newArray[C[array[k]] - 1] = array[k];
        C[array[k]]--;
    }
    return newArray;
}

对比

function countingSort(arr, maxValue) {
    var bucket = new Array(maxValue+1),
        sortedIndex = 0;
        arrLen = arr.length,
        bucketLen = maxValue + 1;

    for (var i = 0; i < arrLen; i++) {
        if (!bucket[arr[i]]) {
            bucket[arr[i]] = 0;
        }
        bucket[arr[i]]++;
    }

    for (var j = 0; j < bucketLen; j++) {
        while(bucket[j] > 0) {
            arr[sortedIndex++] = j;
            bucket[j]--;
        }
    }

    return arr;
}