// 将 a[i] + a[j] + a[k] 改为 (long)a[i] + a[j] + a[k] 即可。
// 此时整个式子将按照精度最高（也就是 long）的标准计算。
static void Main(string[] args)
{
int[] a = new int[4];
a[0] = int.MaxValue;
a[1] = int.MaxValue;
a[2] = int.MinValue;
a[3] = 1;
Console.WriteLine(ThreeSum.Count(a));//2
}
/// <summary>
/// 返回对 n 个随机整数的数组进行一次 ThreeSum 所需的时间。
/// </summary>
/// <param name="n">随机数组的长度。</param>
/// <returns>运行时间，单位为毫秒。</returns>
public static double TimeTrial(int n)
{
var a = new int[n];
var random = new Random(DateTime.Now.Millisecond);
for (var i = 0; i < n; i++)
{
a[i] = random.Next(-MaximumInteger, MaximumInteger);
}
var timer = new Stopwatch();
ThreeSum.Count(a);
return(timer.ElapsedTime());
}
// 由于数组已经排序（从小到大），负数在左侧，正数在右侧。
// TwoSumFaster
// 设最左侧下标为 lo，最右侧下标为 hi。
// 如果 a[lo] + a[hi] > 0, 说明正数太大，hi--。
// 如果 a[lo] + a[hi] < 0，说明负数太小，lo++。
// 否则就找到了一对和为零的整数对，lo++, hi--。
//
// ThreeSumFaster
// 对于数组中的每一个数 a，ThreeSum 问题就等于求剩余数组中所有和为 -a 的 TwoSum 问题。
// 只要在 TwoSumFaster 外层再套一个循环即可。
static void Main(string[] args)
{
char[] split = new char[1] {
'\n'
};
string[] testCases = TestCase.Properties.Resources._1Kints.Split(split, StringSplitOptions.RemoveEmptyEntries);
int[] a = new int[testCases.Length];
for (int i = 0; i < testCases.Length; i++)
{
a[i] = int.Parse(testCases[i]);
}
Array.Sort(a);
Console.WriteLine(TwoSum.Count(a));
Console.WriteLine(TwoSumFaster(a));
Console.WriteLine(ThreeSum.Count(a));
Console.WriteLine(ThreeSumFaster(a));
}
private static void ThreeSumCalc(int count)
{
var arr = ThreeSum.GetRandomArray(count);
var watch = new Stopwatch();
watch.Start();
var result = ThreeSum.Count(arr);
watch.Stop();
var ts = watch.Elapsed;
System.Console.WriteLine();
System.Console.WriteLine($"消耗时间: {ts.TotalMilliseconds} ms ({ts.TotalSeconds} s)");
System.Console.WriteLine($"问题规模: {arr.Length}");
System.Console.WriteLine($"求解结果(三个数和为 0 的个数): {result}");
System.Console.WriteLine();
}
/// <summary>
/// 返回对 n 个随机整数的数组进行一次 ThreeSum 所需的时间。
/// </summary>
/// <param name="n">随机数组的长度。</param>
/// <param name="repeatTimes">重复测试的次数。</param>
/// <returns></returns>
public static double TimeTrial(int n, int repeatTimes)
{
var a = new int[n];
double sum = 0;
var random = new Random(DateTime.Now.Millisecond);
for (var i = 0; i < n; i++)
{
a[i] = random.Next(-MaximumInteger, MaximumInteger);
}
for (var i = 0; i < repeatTimes; i++)
{
var timer = new Stopwatch();
ThreeSum.Count(a);
sum += timer.ElapsedTime();
}
return(sum / repeatTimes);
}
/// <summary>
/// 返回对 n 个随机整数的数组进行一次 ThreeSum 所需的时间。
/// </summary>
/// <param name="n">随机数组的长度。</param>
/// <param name="repeatTimes">重复测试的次数。</param>
/// <returns></returns>
public static double TimeTrial(int n, int repeatTimes)
{
int[] a = new int[n];
double sum = 0;
Random random = new Random(DateTime.Now.Millisecond);
for (int i = 0; i < n; i++)
{
a[i] = random.Next(-MAXIMUM_INTEGER, MAXIMUM_INTEGER);
}
for (int i = 0; i < repeatTimes; i++)
{
Stopwatch timer = new Stopwatch();
ThreeSum.Count(a);
sum += timer.ElapsedTime();
}
return(sum / repeatTimes);
}
static void Main(string[] args)
{
var ints = In.ReadInts("1Kints.txt").ToArray();
Stopwatch watch = new Stopwatch();
watch.Start();
var triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine(String.Format("The number of zero sum triplets is {0} for 1Kints, process performed in {1} seconds.", triplets, watch.Elapsed));
ints = In.ReadInts("2Kints.txt").ToArray();
watch = new Stopwatch();
watch.Start();
triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine(String.Format("The number of zero sum triplets is {0} for 2Kints, process performed in {1} seconds.", triplets, watch.Elapsed));
ints = In.ReadInts("4Kints.txt").ToArray();
watch = new Stopwatch();
watch.Start();
triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine(String.Format("The number of zero sum triplets is {0} for 4Kints, process performed in {1} seconds.", triplets, watch.Elapsed));
ints = In.ReadInts("8Kints.txt").ToArray();
watch = new Stopwatch();
watch.Start();
triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine(String.Format("The number of zero sum triplets is {0} for 8Kints, process performed in {1} seconds.", triplets, watch.Elapsed));
ints = In.ReadInts("16Kints.txt").ToArray();
watch = new Stopwatch();
watch.Start();
triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine(String.Format("The number of zero sum triplets is {0} for 16Kints, process performed in {1} seconds.", triplets, watch.Elapsed));
Console.ReadLine();
}
public void FastVsSlow(string file, int expectedCount, int timeoutInSeconds)
{
string actualFilePath = $"../../data/{file}";
if (!File.Exists(actualFilePath))
{
throw new InvalidOperationException(file);
}
int[] intArray = File.ReadAllLines(actualFilePath).Select(s => int.Parse(s)).ToArray();
var fast = Helper.Time(() => ThreeSumFast.Count(intArray), "3SumFast");
Assert.Equal(expectedCount, fast.Item1);
var slow = Helper.Time(() => ThreeSum.Count(intArray), "3SumSlow");
Assert.Equal(expectedCount, slow.Item1);
Assert.True(fast.Item2 < slow.Item2);
Assert.True(fast.Item2 + slow.Item2 < timeoutInSeconds * 1000);
}
// самые первые занятия, когда показывался подсчет времени
private static void TestTimeComplexityOnKints()
{
/// 1 => 160ms
/// 2 => 1.35s
/// 4 => 10.26s
/// 8 => 1m20s
///
var ints = In.ReadInts("4Kints.txt").ToArray();
var watch = new Stopwatch();
watch.Start();
var triplets = ThreeSum.Count(ints);
watch.Stop();
Console.WriteLine($"The number of \"zero-triplets\" : {triplets}");
Console.WriteLine($"Time taken: {watch.Elapsed:g}");
Console.Read();
}