排序問題相信大家都比較熟悉了。用js簡單寫了一下幾種常用的排序實現。其中使用了es6的一些語法，並且不僅限於數字——支持各種類型的數據的排序。那麽直接上代碼：

function compare (a, b) {
    return (a - b) > 0;
}

// 冒泡排序O(n^2)
const bubbleSort = function (arrayData, compareFn = compare) {
    let len = arrayData.length;
    for (let i = len - 1; i > 0; i--) {
        for (let j = 0; j < i; j++) {
            if (compareFn(arrayData[j], arrayData[j + 1])) {
                [arrayData[j], arrayData[j + 1]] = [arrayData[j + 1], arrayData[j]];
            }
        }
    }
}

// 快速排序 O(n*logn)
function getMid (arrayData) {
    return arrayData[0];
}

const quickSort = function (arrayData, compareFn = compare, getMidFn = getMid) {
    let len = arrayData.length;
    if (len < 2) {
        return arrayData;
    }
    let mid = getMidFn(arrayData);
    let smallGroup = [];
    let largeGroup = [];
    let midGroup = [];
    for (let i = 0; i < len; i++) {
        if (compareFn(mid, arrayData[i])) {
            smallGroup.push(arrayData[i]);
        } else if (compareFn(arrayData[i], mid)) {
            largeGroup.push(arrayData[i]);
        } else {
            midGroup.push(arrayData[i]);
        }
    }
    return [...quickSort(smallGroup, compareFn, getMidFn), ...midGroup, ...quickSort(largeGroup, compareFn, getMidFn)];
}

// 歸並排序 O(n*logn)
const mergeSort = function (arrayData, compareFn = compare) {
    let merge = function (leftArray, rightArray, compareFn) {
        let resultArray = [];
        while (leftArray.length > 0 && rightArray.length > 0) {
            if (compareFn(leftArray[0], rightArray[0])) {
                resultArray.push(leftArray.shift());
            } else {
                resultArray.push(rightArray.shift());
            }
        }
        return resultArray = resultArray.concat(leftArray, rightArray);
    }

    if (arrayData.length <= 1) {
        return arrayData;
    }

    let midIndex = parseInt(arrayData.length / 2);
    let leftArray = arrayData.slice(0, midIndex);
    let rightArray = arrayData.slice(midIndex);
    return merge(mergeSort(leftArray, compareFn), mergeSort(rightArray, compareFn), compareFn);
}

// test codes
// let strArray = ['a', 'c', 'b', 'e', 'd']
// strArray = mergeSort(strArray, (a, b) => {
//     return (a.codePointAt() - b.codePointAt()) > 0;
// });
// console.log(strArray);

// let strArray = ['a', 'c', 'b', 'e', 'd']
// bubbleSort(strArray, (a, b) => {
//  return (a.codePointAt() - b.codePointAt()) > 0;
// });
// console.log(strArray);
 

通過自定義campare函數，用戶可以對任意類型的數據，使用任意的方式進行排序。快速排序允許用戶自定義取中間值的方法，可以結合實際情況，更好的提升排序效率。

js實現冒泡排序（bubble sort）快速排序（quick sort）歸並排序（merge sort）