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using System;
using System.Collections;
using System.Collections.Generic;
using AlgorithmCollection;
using AlgorithmCollection.Recursion;
namespace AlgorithmCollection.Searching
{
public static class SearchingHelper
{
// 二分搜索，返回索引号
// O(logn)
public static int BinarySearch<T>(T[] dataList, T value) where T : IComparable, IEquatable<T>
{
int n = dataList.Length;
int left = 0;
int right = n - 1;
while (left <= right)
{
int middle = (right + left) / 2;
T midValue = dataList[middle];
if (value.Equals(midValue))
return middle;
if (value.CompareTo(midValue) > 0)
left = middle + 1;
if (value.CompareTo(midValue) < 0)
right = middle - 1;
}
return -1; // 没找到
}
public static int BinarySearch<T>(List<T> data, T value) where T : IComparable, IEquatable<T>
{
int index = -1;
RecursionHelper.DC(
() =>
{
DivisionDescriptor div = new DivisionDescriptor();
div.left = 0;
div.right = data.Count - 1;
return div;
},
(DivisionDescriptor div, out DivisionDescriptor[] division) =>
{
int left = div.left;
int right = div.right;
division = new DivisionDescriptor[1];
if(right <= left)
{
division[0].left = left;
division[0].right = right;
return true;
}
int mid = (left + right) / 2;
T midValue = data[mid];
if(midValue.CompareTo(value) > 0)
{
division[0].left = left;
division[0].right = mid - 1;
}
else if (midValue.CompareTo(value) < 0)
{
division[0].left = mid + 1;
division[0].right = right;
}
else
{
division[0].left = mid;
division[0].right = mid;
return true;
}
return false;
},
(DivisionDescriptor div) =>
{
if (data[div.left].CompareTo(value) == 0)
{
index = div.left;
}
}
);
return index;
}
// 查找最大值
// O(n)
public static int FindMax<T>(IList<T> dataList) where T : IList, IComparable
{
int max = 0;
for(int i = 0; i < dataList.Count; ++i)
{
if (dataList[i].CompareTo(dataList[max]) > 0)
max = i;
}
return max;
}
// 查找最小值
// O(n)
public static int FindMin<T>(IList<T> dataList) where T : IList, IComparable
{
int min = 0;
for (int i = 0; i < dataList.Count; ++i)
{
if (dataList[i].CompareTo(dataList[min]) < 0)
min = i;
}
return min;
}
// 找到第n大或者第n小，类比快速排序
// O(n)
public static bool Select<T>(IList<T> data, int n, bool bMin, ref T findValue) where T : IComparable
{
bool suc = false;
T v = default(T);
RecursionHelper.DC(
()=>
{
DivisionDescriptor div = new DivisionDescriptor();
div.left = 0;
div.right = data.Count - 1;
div.userdata = n;
return div;
},
(DivisionDescriptor division, out DivisionDescriptor[] div) =>
{
div = new DivisionDescriptor[1];
int left = division.left;
int right = division.right;
int remain = (int)division.userdata;
if(right <= left)
{
div[0].left = left;
div[0].right = right;
div[0].userdata = remain;
return true;
}
int l = left;
int r = right + 1;
T val = data[l];
while (true)
{
while ((bMin && data[++l].CompareTo(val) <= 0 || !bMin && data[++l].CompareTo(val) >= 0) && l < right);
while ((bMin && data[--r].CompareTo(val) >= 0 || !bMin && data[--r].CompareTo(val) <= 0) && r > left);
if (l >= r)
break;
Algorithms.Swap(ref data, l, r);
}
Algorithms.Swap(ref data, left, r);
int count = r - left + 1;
if(count > remain)
{
div[0].left = left;
div[0].right = r - 1;
div[0].userdata = remain;
}
else if(count < remain)
{
div[0].left = r + 1;
div[0].right = right;
div[0].userdata = remain - count;
}
else
{
div[0].left = r;
div[0].right = r;
div[0].userdata = 0;
return true;
}
return false;
},
(DivisionDescriptor division)=>
{
if((int)division.userdata == 0)
{
int i = division.left;
v = data[i];
suc = true;
}
}
);
if (suc)
{
findValue = v;
return true;
}
return false;
}
}
}
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