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18. 4Sum

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Роман Пытков
2026-03-25 16:58:20 +03:00
parent d99b7d18e3
commit 2464aeff0e
4 changed files with 208 additions and 0 deletions
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11
18. 4Sum/18. 4Sum.csproj Normal file
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<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net10.0</TargetFramework>
<RootNamespace>_18._4Sum</RootNamespace>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>

40
18. 4Sum/Program.cs Normal file
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using System;
using System.Collections.Generic;
using System.Linq;
var sol = new Solution();
var cases = new (int[] nums, int target, int[][] expected)[]
{
// (new[] { 1, 0, -1, 0, -2, 2 }, 0, new[]
// {
// new[] { -2, -1, 1, 2 },
// new[] { -2, 0, 0, 2 },
// new[] { -1, 0, 0, 1 }
// }),
// (new[] { 2, 2, 2, 2, 2 }, 8, new[]
// {
// new[] { 2, 2, 2, 2 }
// }),
// (new[] { -3, -1, 0, 2, 4, 5 }, 2, new[]
// {
// new[] { -3, -1, 2, 4 }
// }),
(new[] { 1000000000, 1000000000, 1000000000, 1000000000 }, -294967296, Array.Empty<int[]>())
};
foreach (var (nums, target, expected) in cases)
{
var actual = sol.FourSum(nums, target);
Console.WriteLine($"nums={FormatArray(nums)}, target={target} -> {FormatResults(actual)} (expected: {FormatResults(expected)})");
}
static string FormatArray(int[] nums)
{
return $"[{string.Join(",", nums)}]";
}
static string FormatResults(IList<IList<int>> results)
{
return "[" + string.Join(",", results.Select(r => $"[{string.Join(",", r)}]")) + "]";
}

143
18. 4Sum/Solution.cs Normal file
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public class Solution
{
record struct TwoSumSource(int A, int B)
{
public override string ToString()
{
return $"({A}+{B}={A + B})";
}
}
record struct AnswerRow(int? N0 = null, int? N1 = null, int? N2 = null, int? N3 = null)
{
public void PushNum(int num)
{
if (N0 == null)
{
N0 = num;
}
else if (N1 == null)
{
N1 = num;
if (N0 > N1)
{
(N0, N1) = (N1, N0);
}
}
else if (N2 == null)
{
N2 = num;
if (N1 > N2)
{
(N1, N2) = (N2, N1);
}
if (N0 > N1)
{
(N0, N1) = (N1, N0);
}
}
else if (N3 == null)
{
N3 = num;
if (N2 > N3)
{
(N2, N3) = (N3, N2);
}
if (N1 > N2)
{
(N1, N2) = (N2, N1);
}
if (N0 > N1)
{
(N0, N1) = (N1, N0);
}
}
else if (num < N3)
{
N3 = num;
if (N2 > N3)
{
(N2, N3) = (N3, N2);
}
if (N1 > N2)
{
(N1, N2) = (N2, N1);
}
if (N0 > N1)
{
(N0, N1) = (N1, N0);
}
}
}
}
public IList<IList<int>> FourSum(int[] nums, int target)
{
var dict = new Dictionary<int, int>();
// суммы из двух слагаемых, все возможные
var twoSums = new Dictionary<long, HashSet<TwoSumSource>>();
for (var i = 0; i < nums.Length; i++)
{
var num1 = nums[i];
dict.TryAdd(num1, 0);
dict[num1]++;
for (var j = i + 1; j < nums.Length; j++)
{
var num2 = nums[j];
var sum = num1 + num2;
twoSums.TryAdd(sum, new HashSet<TwoSumSource>());
twoSums[sum].Add(new TwoSumSource() { A = num1, B = num2 });
}
}
var rows = new HashSet<AnswerRow>();
// словарь для требуемоего количества чисел
var needDict = new Dictionary<int, int>();
foreach (var kp1 in dict)
{
var needThreeSum = target - kp1.Key;
needDict.TryAdd(kp1.Key, 0);
needDict[kp1.Key]++;
foreach (var kp2 in dict)
{
needDict.TryAdd(kp2.Key, 0);
needDict[kp2.Key]++;
var needTwoSum = (long)needThreeSum - kp2.Key;
if (twoSums.TryGetValue(needTwoSum, out var curTwoSums))
{
foreach (var curTwoSum in curTwoSums)
{
needDict.TryAdd(curTwoSum.A, 0);
needDict[curTwoSum.A]++;
needDict.TryAdd(curTwoSum.B, 0);
needDict[curTwoSum.B]++;
if (needDict.All(kp => dict[kp.Key] >= kp.Value))
{
var row = new AnswerRow();
row.PushNum(kp1.Key);
row.PushNum(kp2.Key);
row.PushNum(curTwoSum.A);
row.PushNum(curTwoSum.B);
rows.Add(row);
}
needDict[curTwoSum.A]--;
needDict[curTwoSum.B]--;
}
}
needDict[kp2.Key]--;
}
needDict.Clear();
}
var answer = new List<IList<int>>(rows.Count);
foreach (var row in rows)
answer.Add(new List<int> { row.N0!.Value, row.N1!.Value, row.N2!.Value, row.N3!.Value });
return answer;
}
}

14
Leetcode.sln
View File

@@ -183,6 +183,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "2906. Construct Product Mat
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "3546. Equal Sum Grid Partition I", "3546. Equal Sum Grid Partition I\3546. Equal Sum Grid Partition I.csproj", "{8533B947-4274-46C9-8EEA-1439778FEE32}"
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "18. 4Sum", "18. 4Sum\18. 4Sum.csproj", "{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
@@ -1273,6 +1275,18 @@ Global
{8533B947-4274-46C9-8EEA-1439778FEE32}.Release|x64.Build.0 = Release|Any CPU
{8533B947-4274-46C9-8EEA-1439778FEE32}.Release|x86.ActiveCfg = Release|Any CPU
{8533B947-4274-46C9-8EEA-1439778FEE32}.Release|x86.Build.0 = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|Any CPU.Build.0 = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|x64.ActiveCfg = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|x64.Build.0 = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|x86.ActiveCfg = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Debug|x86.Build.0 = Debug|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|Any CPU.ActiveCfg = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|Any CPU.Build.0 = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|x64.ActiveCfg = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|x64.Build.0 = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|x86.ActiveCfg = Release|Any CPU
{0AF9E85C-7CCC-4E82-80B6-39931EA17D52}.Release|x86.Build.0 = Release|Any CPU
EndGlobalSection
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE