快速排序(演化版by数组)

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基础原始快速排序(进行了优化，保持了稳定性)

import edu.princeton.cs.algs4.StdOut;import edu.princeton.cs.algs4.StdRandom;public class QuickSort {    private int[] a;    public QuickSort(int N)    {        a = new int[N];        for (int i = 0; i < N; ++i)            a[i] = StdRandom.uniform(-15 * N,15 * N);    }    public QuickSort(int[] b)    {        a = new int[b.length];        for (int i = 0; i < a.length; ++i)            a[i] = b[i];    }    public int partition(int lo,int hi)    {        int i = lo,j = hi + 1;        int v = a[lo];        while (true)        {            while (a[lo] >= a[++i]) if (i == hi) break;            while (a[lo] <= a[--j]) if (j == lo) break;            if (i >= j) break;            int temp = a[j];            a[j] = a[i];            a[i] = temp;        }        int temp = a[j];        a[j] = a[lo];        a[lo] = temp;        return j;    }    public void sort(int lo,int hi)    {        if (hi <= lo) return;        int get = partition(lo,hi);        sort(lo,get - 1);        sort(get + 1,hi);    }    public void sort()    {        sort(0,a.length - 1);    }    public void display()    {        for (int i = 0; i < a.length; ++i)            StdOut.print(a[i] + " ");        StdOut.println();    }}

小数组时快速排序比插入排序慢，再次优化

import edu.princeton.cs.algs4.StdOut;import edu.princeton.cs.algs4.StdRandom;public class QuickAndInsert {    private int[] a;    public QuickAndInsert(int N)    {        a = new int[N];        for (int i = 0; i < N; ++i)            a[i] = StdRandom.uniform(-15 * N,15 * N);    }    public QuickAndInsert(int[] b)    {        a = new int[b.length];        for (int i = 0; i < a.length; ++i)            a[i] = b[i];    }    public int partition(int lo,int hi)    {        int i = lo,j = hi + 1;        while (true)        {            while (a[lo] >= a[++i]) if (i == hi) break;            while (a[lo] <= a[--j]) if (j == lo) break;            if (i >= j) break;            int temp = a[i];            a[i] = a[j];            a[j] = temp;        }        int temp = a[lo];        a[lo] = a[j];        a[j] = temp;        return j;    }    public void InsertSort(int lo,int hi)    {        for (int i = lo; i < hi; ++i)        {            int j = i + 1;            int temp = a[j];            while (j > lo && temp < a[j - 1])            {                a[j] = a[j - 1];                --j;            }            a[j] = temp;        }    }    public void sort(int lo,int hi)    {        if (hi <= lo) return;        if (hi - lo <= 5)        {            InsertSort(lo,hi);            return;        }        int get = partition(lo,hi);        sort(lo,get - 1);        sort(get + 1,hi);    }    public void sort()    {        sort(0,a.length - 1);    }    public void display()    {        for (int i = 0; i < a.length; ++i)            StdOut.print(a[i] + " ");        StdOut.println();    }}

重复元素过多，会将重复元素数组也切分未免太过浪费，再次进行优化，此次优化的排序方法成为 三向切分的快速排序

import edu.princeton.cs.algs4.StdOut;import edu.princeton.cs.algs4.StdRandom;public class Quick3Way {    private int[] a;    public Quick3Way(int N)    {        a = new int[N];        for (int i = 0; i < N; ++i)            a[i] = StdRandom.uniform(-15*N,15*N);    }    public Quick3Way(int[] b)    {        a = new int[b.length];        for (int i = 0; i < a.length; ++i)            a[i] = b[i];    }    public void sort(int lo,int hi)    {        if (lo >= hi) return;        int le = lo,i = lo + 1,he = hi;        int v = a[lo];        while (i <= he)        {            if (v > a[i])            {                int temp = a[le];                a[le++] = a[i];                a[i++] = temp;            }            else if (v < a[i])            {                int temp = a[i];                a[i] = a[he];                a[he--] = temp;            }            else                ++i;        }        sort(lo,le - 1);        sort(he + 1,hi);    }    public void sort()    {        sort(0,a.length - 1);    }    public void display()    {        for (int i = 0; i < a.length; ++i)            StdOut.print(a[i] + " ");        StdOut.println();    }}

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