Question

我是算法的新手，我很困惑我的代码中的错误在哪里作为一个赋值。我正在尝试在Python 3中实现一个快速排序算法，它在数组中处理相同的值。

这是一个快速排序功能（代表阵列）：

def randomized_quick_sort(a, l, r):
    if l >= r:
        return
    k = random.randint(l, r)
    a[l], a[k] = a[k], a[l]
    m1, m2 = partition3(a, l, r)
    randomized_quick_sort(a, l, m1 - 1);
    randomized_quick_sort(a, m2 + 1, r);

这是我的分区功能：

def partition3(a, l, r):
    x, j, t = a[l], l, r
    for i in range(l + 1, r + 1):
        if a[i] < x:
            j +=1
            a[i], a[j] = a[j], a[i]
        elif a[i] > x:
            a[i], a[t] = a[t], a[i]
            t -=1
        else:
            j +=1
    a[l], a[j] = a[j], a[l]
    return j, t

Answer 1

你应该纠正你的分区功能：

这是一个有效的例子：

var webpack = require('webpack');

var commonsPlugin =
    new webpack.optimize.CommonsChunkPlugin('common.js');

module.exports = {

    entry: {
        main: './src/scripts/app/index.js',
        vendor: [
            "./src/scripts/lib/jquery.min.js",
            "./src/scripts/lib/jquery.qtip/jquery.qtip.min.js",
            "./src/scripts/lib/jquery.qtip/imagesloaded.pkg.min.js"
        ]
    },

    output: {
        path: __dirname + '/build',
        publicPath: '/',
        filename: '[name]-[hash].js'
    },

    node: {
        filename: true,
        process: true,
        global: true
    },

    resolve: {
        extensions: [
            '', // Any
            '.js', '.json', // Scripts & Scripts Data
            '.vue', // Vue
            'css', 'styl', // Styles
            'png', 'jpg', 'gif', 'svg' // Images
        ]
    },

    module: {
        loaders: [{
            test: /\.vue$/,
            loader: 'vue'
        }, {
            test: /\.js$/,
            loader: 'babel'
        }, {
            test: /\.css$/,
            loader: ['style', 'css']
        }, {
            test: /\.styl$/,
            loader: ['style', 'css', 'stylus']
        },{
             test: /\.(png|jpg|gif|svg)$/,
             loader: 'url',
             query: {
                 // limit for base64 inlining in bytes
                 // Min 8KB
                 limit: 8 * 1024,

                 // custom naming format if file is larger than
                 // the threshold
                 name: '[name].[ext]?[hash]'
             }
        }]
    },

    plugins: [
        commonsPlugin
    ]
};

Answer 2

这是python中一个简单的快速实现。虽然它仍然是nlogn，但可以进行一系列性能优化。例如，可以在单次传递中进行分区为更小，相等，更大，而不是数组的3次传递。

def qsort(arr):
    if len(arr) <= 1: return arr
    pivot = arr[0]
    less    = [x for x in arr if x < pivot]
    equal   = [x for x in arr if x == pivot]
    greater = [x for x in arr if x > pivot]
    return qsort(less) + equal + qsort(greater)

要使该分区在数组的一次传递中发生，请创建一个如下的辅助函数：

def partition(arr, pivot):
    less, equal, greater = [], [], []
    for val in arr:
        if val  < pivot: less.append(val)
        if val == pivot: equal.append(val)
        if val  > pivot: greater.append(val)
    return less, equal, greater

def qsort(arr):
    if len(arr) <= 1: return arr
    pivot = arr[0]
    less, equal, greater = partition(arr, pivot)
    return qsort(less) + equal + qsort(greater)

Answer 3

for loop

的另一个实现

def partition3(a, l, r):
    x = a[l]
    m1 = l
    m2 = l
    i = m1
    for i in range(l + 1, r + 1):
        if a[i] < x:
            a[i], a[m1] = a[m1], a[i]
            a[i], a[m2+1] = a[m2+1], a[i]
            m1 += 1
            m2 += 1
        elif a[i] == x:
            a[i], a[m2+1] = a[m2+1], a[i]
            m2 += 1
    return m1, m2

实施3向快速排序

3 个答案: