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Program.cs
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Program.cs
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//创建长度比nums长一位的数组record,用于记录数字的个数。遍历nums,将当前数字在record的记录加一。
//遍历record,将记录为2的数字加入res。
using System;
using System.Collections.Generic;
using System.Linq;
namespace FindAllDuplicatesInAnArray
{
class Program
{
static void Main(string[] args)
{
int[] nums = {4, 3, 2, 7, 8, 2, 3, 1};
Console.WriteLine(FindDuplicates_NoExtraSpace1(nums));
}
static IList<int> FindDuplicates(int[] nums)
{
List<int> res = new List<int>();
int[] record = new int[nums.Length + 1];
for (int i = 0; i < nums.Length; i++)
record[nums[i]]++;
for (int i = 0; i < record.Length; i++)
if (record[i] == 2)
res.Add(i);
return res;
}
static IList<int> FindDuplicates_NoExtraSpace1(int[] nums)
{
var res = new HashSet<int>();
int index = 0;
while (index < nums.Length)
{
int num = nums[index];
if (num != index + 1)
{
if (num == nums[num - 1])
{
res.Add(num);
index++;
}
else
{
nums[index] = nums[num - 1];
nums[num - 1] = num;
}
}
else
index++;
}
return res.ToList();
}
static IList<int> FindDuplicates_NoExtraSpace2(int[] nums)
{
var res = new List<int>();
for (int i = 0; i < nums.Length; i++)
{
var index = Math.Abs(nums[i]) - 1;
if (nums[index] < 0)
res.Add(index + 1);
else
nums[index] = -nums[index];
}
return res;
}
}
}