优化这个C#算法
本文关键字:算法 优化 | 更新日期: 2023-09-27 17:59:56
这是一个算法问题,我有解决方案,但它有性能问题。
问题描述
有n个变量和m个要求。需求表示为(x<=y),这意味着第x个变量必须小于或等于第y个变量。为每个变量指定小于10的非负数。请计算有多少不同的作业符合所有要求。两个赋值是不同的,当且仅当在这两个赋值中至少有一个变量被赋予不同的编号。在1007之前将答案模块化。
输入格式:
输入的第一行包含两个整数n和m。然后跟随m行,每行包含2个空格分隔的整数x和y,这意味着一个要求(x<=y)。
输出格式:
在一行中输出答案。
限制:
0<n<14
0<m<200
0<=x、 y<n
样本输入:
6 7
1 3
0 1
2 4
0 4
2 5
3 4
0 2
样本输出:
1000
以下是我的解决方案。当n=13和m=199时,得到结果需要很长时间,但可接受的时间是5秒。
那么,有人能想出更好的方法来进一步优化吗?非常感谢。
我目前的解决方案:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication81
{
class Program
{
const int N = 10;
static List<Condition> condition = new List<Condition>();
static void Main(string[] args)
{
string[] line1 = Console.ReadLine().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
int n = int.Parse(line1[0]);
int m = int.Parse(line1[1]);
for (int i = 0; i < m; i++)
{
string[] line = Console.ReadLine().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
condition.Add(new Condition()
{
X = int.Parse(line[0]),
Y = int.Parse(line[1])
});
}
//
List<int[]> rlist = new List<int[]>();
for (int j = 0; j < N; j++)
{
int[] assignments = new int[n];
for (int i = 0; i < n; i++)
assignments[i] = -1;
assignments[0] = j;
rlist.Add(assignments);
}
for (int j = 1; j < n; j++)
{
List<int[]> rlist2 = new List<int[]>(rlist.Count*5);
for (int k = 0; k < rlist.Count; k++)
{
for (int l = 0; l < N; l++)
{
rlist[k][j] = l;
if (CanPassCondition(rlist[k]))
rlist2.Add((int[])rlist[k].Clone());
}
}
rlist = rlist2;
}
Console.Write(rlist.Count % 1007);
}
private static bool CanPassCondition(int[] p)
{
foreach (var c in condition)
{
if (p[c.X] == -1 || p[c.Y] == -1)
continue;
if (p[c.X] > p[c.Y])
return false;
}
return true;
}
}
class Condition
{
public int X;
public int Y;
public override string ToString()
{
return string.Format("x:{0}, y:{1}", X, Y);
}
}
}
这里有一个Java解决方案,即使n=13,m=199:,它也能很快地工作
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;
public class Assignments
{
private static Map <String, Long> solutions = new HashMap <String, Long> ();
private static boolean [][] constraints;
private static long solve (int n, int [] low, int [] high)
{
StringBuilder sb = new StringBuilder ();
for (int i = 0; i < n; i++)
{
sb.append (low [i]);
sb.append (high [i]);
}
String signature = sb.toString ();
Long result = solutions.get (signature);
if (result == null)
{
result = Long.valueOf (doSolve (n, low, high));
solutions.put (signature, result);
}
return result.longValue ();
}
private static long doSolve (int n, int [] low, int [] high)
{
if (n == 0) return 1;
else
{
long result = 0;
for (int i = low [n - 1]; i <= high [n - 1]; i++)
{
int [] l = new int [n - 1];
int [] h = new int [n - 1];
for (int j = 0; j < n - 1; j++)
{
l [j] = constraints [n - 1][j] ? Math.max (low [j], i) : low [j];
h [j] = constraints [j][n - 1] ? Math.min (high [j], i) : high [j];
}
result += solve (n - 1, l, h);
}
return result;
}
}
public static void main(String[] args) throws Exception
{
BufferedReader reader =
new BufferedReader (
new InputStreamReader(System.in));
String nm = reader.readLine ();
String [] pair = nm.split(" ");
int n = Integer.parseInt(pair [0]);
int m = Integer.parseInt(pair [1]);
constraints = new boolean [n][];
for (int i = 0; i < n; i++)
constraints [i] = new boolean [n];
int [] low = new int [n];
int [] high = new int [n];
for (int i = 0; i < n; i++)
high [i] = 9;
for (int i = 0; i < m; i++)
{
String ab = reader.readLine();
pair = ab.split (" ");
int a = Integer.parseInt(pair [0]);
int b = Integer.parseInt(pair [1]);
constraints [a][b] = true;
}
System.out.println(solve (n, low, high));
}
}
事实上,一旦你有13个变量,你可能只有156(13*12)个有意义的约束,但是。
样本输入:
13 1
3 8
输出:
5500000000000
另一个样本输入:
13 12
0 1
1 2
2 3
3 4
4 5
5 6
6 7
7 8
8 9
9 10
10 11
11 12
输出:
497420