/// <summary>
/// Rearrange the array,so the result is random
/// </summary>
/// <param name="arr"></param>
public static void RandomRearrange(T[] arr)
{
if (arr == null || arr.Length <= 1)
{
return;
}
Random rand = new Random();
for (int i = 0; i < arr.Length - 1; i++)
{
int index = rand.Next(i, arr.Length);
SortCommons <T> .Exchange(arr, i, index);
}
}
/// <summary>
/// hi must >= lo, and sort arr[lo...hi] in place. Doesn't affect the element out of [lo,hi]
/// </summary>
/// <param name="arr"></param>
/// <param name="lo"></param>
/// <param name="hi"></param>
/// <returns></returns>
public static T[] Sort(T[] arr, int lo, int hi)
{
for (int i = hi; i > lo; i--)
{
for (int j = lo; j < i; j++)
{
if (arr[j].CompareTo(arr[j + 1]) > 0)
{
SortCommons <T> .Exchange(arr, j, j + 1);
}
}
}
return(arr);
}
/// <summary>
/// hi must >= lo, and sort arr[lo...hi] in place. Doesn't affect the element out of [lo,hi]
/// </summary>
/// <param name="arr"></param>
/// <param name="lo"></param>
/// <param name="hi"></param>
/// <returns></returns>
public static T[] Sort(T[] arr, int lo, int hi)
{
for (int i = lo; i < hi; i++)
{
int minIndex = i;
for (int j = i + 1; j <= hi; j++)
{
if (arr[minIndex].CompareTo(arr[j]) > 0)
{
minIndex = j;
}
}
SortCommons <T> .Exchange(arr, minIndex, i);
}
return(arr);
}
/// <summary>
/// Divide A[p...r] into two part A[p...q-1] and [q+1...r] such that each element of A[p...q-1] is less than or equal to A[q] , which is ,in turn, less than each element of A[q+1....r]
/// </summary>
/// <param name="arr"></param>
/// <param name="lo">you should guarantee the availabity of the index</param>
/// <param name="hi"></param>
/// <returns></returns>
public static int Partition2(T[] arr, int lo, int hi)
{
T tmp = arr[hi];
//let hi as pivot. from low postion, find the one lower than the pivot and move it to low position
int q = lo - 1;
for (int i = lo; i < hi; i++)
{
if (arr[i].CompareTo(tmp) <= 0)
{
q++;
SortCommons <T> .Exchange(arr, q, i);
}
}
SortCommons <T> .Exchange(arr, q + 1, hi);
return(q + 1);
}
/// <summary>
/// heapsort: it runs in place and runs at n(lgn)
/// </summary>
/// <param name="arr"></param>
public static T[] Sort(params T[] arr)
{
if (arr == null || arr.Length <= 1)
{
return(arr);
}
BuildMaxHeap(arr);
int heapsize = arr.Length;
for (int i = heapsize; i > 1; i--)
{
heapsize--;
SortCommons <T> .Exchange(arr, heapsize, 0);
Sink(arr, 0, heapsize);
}
return(arr);
}
/// <summary>
/// partition the subarray a[lo .. hi] by returning an index j. so that a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
/// </summary>
/// <param name="a"></param>
/// <param name="lo"></param>
/// <param name="hi"></param>
/// <returns></returns>
public static int Partition4(T[] a, int lo, int hi)
{
int i = lo;
int j = hi + 1;
T v = a[lo];
while (true)
{
// find item on lo to swap
//找到第一个比lo大的元素位置
while (a[++i].CompareTo(v) <= 0)
{
if (i == hi)
{
break;
}
}
// find item on hi to swap
while (v.CompareTo(a[--j]) <= 0)
{
if (j == lo)
{
break; // redundant since a[lo] acts as sentinel
}
}
// check if pointers cross
if (i >= j)
{
break;
}
SortCommons <T> .Exchange(a, i, j);
}
// put v = a[j] into position
SortCommons <T> .Exchange(a, lo, j);
// with a[lo .. j-1] <= a[j] <= a[j+1 .. hi]
return(j);
}
/// <summary>
/// lets the value at arr[i] “float down” in the max-heap so that the subtree rooted at index i obeys the max-heap property.
/// it runs at O(lgn)
/// </summary>
/// <param name="arr" />
/// <param name="i"></param>
/// <param name="heapsize"> </param>
private static void Sink(T[] arr, int i, int heapsize)
{
int left = Left(i);
int right = Right(i);
int max = i;
if (left < heapsize && arr[left].CompareTo(arr[max]) > 0)
{
max = left;
}
if (right < heapsize && arr[right].CompareTo(arr[max]) > 0)
{
max = right;
}
if (max != i)
{
SortCommons <T> .Exchange(arr, max, i);
Sink(arr, max, heapsize);
}
}
/// <summary>
/// Divide A[p...r] into two part A[p...q-1] and [k+1...r] such that each element of A[p...q-1] is less than A[q...k] ,a[q...k] are equal, which is ,in turn, less than each element of A[q+1....r]
/// </summary>
/// <param name="arr"></param>
/// <param name="lo">you should guarantee the availabity of the index</param>
/// <param name="hi"></param>
/// <param name="q"> </param>
/// <param name="k"> </param>
/// <returns></returns>
public static void Partition3(T[] arr, int lo, int hi, out int q, out int k)
{
q = lo;
k = hi;
T temp = arr[lo];
int i = lo;
while (i <= k)
{
int cmp = arr[i].CompareTo(temp);
if (cmp < 0)
{
SortCommons <T> .Exchange(arr, q ++, i ++);
}
else if (cmp > 0)
{
SortCommons <T> .Exchange(arr, k --, i);
}
else
{
i++;
}
}
}
