var bubbleSort = function(arr) {

 for (var i = 0, len = arr.length; i < len - 1; i++) {
 for (var j = i + 1; j < len; j++) {
 if (arr[i] > arr[j]) {
 var temp = arr[i];
 arr[i] = arr[j];
 arr[j] = temp;
 }
 }
 }

 return arr;
};

var selectSort = function(arr) {

 var min;
 for (var i = 0; i < arr.length - 1; i++) {
 min = i;
 for (var j = i + 1; j < arr.length; j++) {
 if (arr[min] > arr[j]) {
 min = j;
 }
 }
 if (i != min) {
 swap(arr, i, min);
 }
 console.log(i + 1, ": " + arr);
 }
 return arr;
};

function swap(arr, index1, index2) {
 var temp = arr[index1];
 arr[index1] = arr[index2];
 arr[index2] = temp;
};

var insertSort = function(arr) {
 var len = arr.length,
 key;
 for (var i = 1; i < len; i++) {
 var j = i;
 key = arr[j];
 while (--j > -1) {
 if (arr[j] > key) {
 arr[j + 1] = arr[j];
 } else {
 break;
 }
 }
 arr[j + 1] = key;
 }
 return arr;
};

function shellSort(arr) {
 if (arr.length < 2) {
 return arr;
 };
 var n = arr.length;
 for (gap = Math.floor(n / 2); gap > 0; gap = Math.floor(gap /= 2)) {
 for (i = gap; i < n; ++i) {
 for (j = i - gap; j >= 0 && arr[j + gap] < arr[j]; j -= gap) {
 temp = arr[j];
 arr[j] = arr[j + gap];
 arr[j + gap] = temp;
 }
 }
 }
 return arr;
};

function merge(left, right) {
 var result = [];
 while (left.length > 0 && right.length > 0) {
 if (left[0] < right[0]) {
 // shift()方法用于把數組的第一個元素從其中刪除，并返回第一個元素的值
 result.push(left.shift());
 } else {
 result.push(right.shift());
 }
 }
 return result.concat(left).concat(right);
}

function mergeSort(arr) {
 if (arr.length == 1) {
 return arr;
 }
 var middle = Math.floor(arr.length / 2),
 left = arr.slice(0, middle),
 right = arr.slice(middle);
 return merge(mergeSort(left), mergeSort(right));
}

var quickSort = function(arr) {　　
 if (arr.length <= 1) {
 return arr;
 }

 var pivotIndex = Math.floor(arr.length / 2);　
 var pivot = arr.splice(pivotIndex, 1)[0];

 var left = [];
 var right = [];　　
 for (var i = 0; i < arr.length; i++) {　　　
 if (arr[i] < pivot) {　　　　　　
 left.push(arr[i]);　　　　
 } else {　　　　　　
 right.push(arr[i]);　　　　
 }　
 }　　
 return quickSort(left).concat([pivot], quickSort(right));

};