# js算法

1.1 冒泡排序

``````function bubbleSort(arr) {
var len = arr.length;
for (var i = 0; i < len - 1; 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;
}``````

1.2 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;
}``````

1.3 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;
}``````

1.4 希尔排序

``````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;
}``````

1.5 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;
}``````

1.6 快速排序

“快速排序（Quicksort）是对冒泡排序算法的一种改进。”

``````function quickSort(arr, left, right) {
var len = arr.length,
partitionIndex,
left = typeof left != 'number' ? 0 : left,
right = typeof right != 'number' ? len - 1 : right;

if (left < right) {
partitionIndex = partition(arr, left, right);
quickSort(arr, left, partitionIndex-1);
quickSort(arr, partitionIndex+1, right);
}
return arr;
}

function partition(arr, left ,right) {     // 分区操作
var pivot = left,                      // 设定基准值（pivot）
index = pivot + 1;
for (var i = index; i <= right; i++) {
if (arr[i] < arr[pivot]) {
swap(arr, i, index);
index++;
}
}
swap(arr, pivot, index - 1);
return index-1;
}

function swap(arr, i, j) {
var temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
function partition2(arr, low, high) {
let pivot = arr[low];
while (low < high) {
while (low < high && arr[high] > pivot) {
--high;
}
arr[low] = arr[high];
while (low < high && arr[low] <= pivot) {
++low;
}
arr[high] = arr[low];
}
arr[low] = pivot;
return low;
}

function quickSort2(arr, low, high) {
if (low < high) {
let pivot = partition2(arr, low, high);
quickSort2(arr, low, pivot - 1);
quickSort2(arr, pivot + 1, high);
}
return arr;
}``````

1.7 堆排序

``````var len;    // 因为声明的多个函数都需要数据长度，所以把len设置成为全局变量

function buildMaxHeap(arr) {   // 建立大顶堆
len = arr.length;
for (var i = Math.floor(len/2); i >= 0; i--) {
heapify(arr, i);
}
}

function heapify(arr, i) {     // 堆调整
var left = 2 * i + 1,
right = 2 * i + 2,
largest = i;

if (left < len && arr[left] > arr[largest]) {
largest = left;
}

if (right < len && arr[right] > arr[largest]) {
largest = right;
}

if (largest != i) {
swap(arr, i, largest);
heapify(arr, largest);
}
}

function swap(arr, i, j) {
var temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}

function heapSort(arr) {
buildMaxHeap(arr);

for (var i = arr.length-1; i > 0; i--) {
swap(arr, 0, i);
len--;
heapify(arr, 0);
}
return arr;
}``````

1.8 计数排序

``````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;
}``````

1.9 桶排序

``````function bucketSort(arr, bucketSize) {
if (arr.length === 0) {
return arr;
}

var i;
var minValue = arr[0];
var maxValue = arr[0];
for (i = 1; i < arr.length; i++) {
if (arr[i] < minValue) {
minValue = arr[i];                // 输入数据的最小值
} else if (arr[i] > maxValue) {
maxValue = arr[i];                // 输入数据的最大值
}
}

//桶的初始化
var DEFAULT_BUCKET_SIZE = 5;            // 设置桶的默认数量为5
bucketSize = bucketSize || DEFAULT_BUCKET_SIZE;
var bucketCount = Math.floor((maxValue - minValue) / bucketSize) + 1;
var buckets = new Array(bucketCount);
for (i = 0; i < buckets.length; i++) {
buckets[i] = [];
}

//利用映射函数将数据分配到各个桶中
for (i = 0; i < arr.length; i++) {
buckets[Math.floor((arr[i] - minValue) / bucketSize)].push(arr[i]);
}

arr.length = 0;
for (i = 0; i < buckets.length; i++) {
insertionSort(buckets[i]);                      // 对每个桶进行排序，这里使用了插入排序
for (var j = 0; j < buckets[i].length; j++) {
arr.push(buckets[i][j]);
}
}

return arr;
}``````

1.10 基数排序

``````//LSD Radix Sort
var counter = [];
var mod = 10;
var dev = 1;
for (var i = 0; i < maxDigit; i++, dev *= 10, mod *= 10) {
for(var j = 0; j < arr.length; j++) {
var bucket = parseInt((arr[j] % mod) / dev);
if(counter[bucket]==null) {
counter[bucket] = [];
}
counter[bucket].push(arr[j]);
}
var pos = 0;
for(var j = 0; j < counter.length; j++) {
var value = null;
if(counter[j]!=null) {
while ((value = counter[j].shift()) != null) {
arr[pos++] = value;
}
}
}
}
return arr;
}``````