C# 如何检查我的数组中是否有重复的值？
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How do I check if my array has repeated values inside it?
提问by puretppc
So here is my array.
所以这是我的数组。
double[] testArray = new double[10];
// will generate a random numbers from 1-20, too lazy to write the code
I want to make a search loop to check if any values are being repeated. How do I do that?
我想做一个搜索循环来检查是否有重复的值。我怎么做？
I would prefer not to use any special built-in methods since this is a small array.
我不想使用任何特殊的内置方法，因为这是一个小数组。
采纳答案by p.s.w.g
You could do this with a little Linq:
你可以用一个小的 Linq 来做到这一点：
if (testArray.Length != testArray.Distinct().Count())
{
Console.WriteLine("Contains duplicates");
}
The Distinctextension method removes any duplicates, and Countgets the size of the result set. If they differ at all, then there are some duplicates in the list.
该Distinct扩展方法除去任何重复，并且Count得到的结果集的大小。如果它们完全不同，则列表中有一些重复项。
Alternatively, here's more complicated query, but it may be a bit more efficient:
或者，这里有更复杂的查询，但它可能更有效：
if (testArray.GroupBy(x => x).Any(g => g.Count() > 1))
{
Console.WriteLine("Contains duplicates");
}
The GroupBymethod will group any identical elements together, and Anyreturn trueif any of the groups has more than one element.
该GroupBy方法将任何相同的元素组合在一起，如果任何组有多个元素，则Any返回true。
Both of the above solutions work by utilizing a HashSet<T>, but you can use one directly like this:
上述两种解决方案都通过使用 a 来工作HashSet<T>，但您可以像这样直接使用一个：
if (!testArray.All(new HashSet<double>().Add))
{
Console.WriteLine("Contains duplicates");
}
Or if you prefer a solution that doesn't rely on Linq at all:
或者，如果您更喜欢完全不依赖 Linq 的解决方案：
var hashSet = new HashSet<double>();
foreach(var x in testArray)
{
if (!hashSet.Add(x))
{
Console.WriteLine("Contains duplicates");
break;
}
}
回答by helb
Use this:
用这个：
bool CheckUniqueness(double[] values)
{
var uniqueValues = new HashSet<double>();
foreach (double d in values)
{
if(uniqueValues.Contains(d))
{
return false;
}
uniqueValues.Add(d);
}
return true;
}
回答by P_P
With (OP) 10 random doubles quite fast. The chance of a repeat: ~0.000002 %.
使用 (OP) 10 随机加倍非常快。重复的几率：~0.000002 %。
static bool repeat(double[] a)
{
return
a[0] == a[1] || a[0] == a[2] || a[0] == a[3] || a[0] == a[4] ||
a[0] == a[5] || a[0] == a[6] || a[0] == a[7] || a[0] == a[8] ||
a[0] == a[9] || a[1] == a[2] || a[1] == a[3] || a[1] == a[4] ||
a[1] == a[5] || a[1] == a[6] || a[1] == a[7] || a[1] == a[8] ||
a[1] == a[9] || a[2] == a[3] || a[2] == a[4] || a[2] == a[5] ||
a[2] == a[6] || a[2] == a[7] || a[2] == a[8] || a[2] == a[9] ||
a[3] == a[4] || a[3] == a[5] || a[3] == a[6] || a[3] == a[7] ||
a[3] == a[8] || a[3] == a[9] || a[4] == a[5] || a[4] == a[6] ||
a[4] == a[7] || a[4] == a[8] || a[4] == a[9] || a[5] == a[6] ||
a[5] == a[7] || a[5] == a[8] || a[5] == a[9] || a[6] == a[7] ||
a[6] == a[8] || a[6] == a[9] || a[7] == a[8] || a[7] == a[9] ||
a[8] == a[9];
}
More general, with 10 numbers ~2 times slower than above,
but ~7 times faster than the hashset approach.
更一般的，10 个数字比上面慢 2 倍，
但比 hashset 方法快 7 倍。
static bool repeat(double[] a)
{
int k = a.Length - 1;
if (k < 70)
{
double aj;
for (int i = 0, j; i < k; )
{
for (aj = a[k--], j = k; j >= i; j--)
if (aj == a[j]) return true;
for (aj = a[i++], j = i; j <= k; j++)
if (aj == a[j]) return true;
}
return false;
}
var h = new HashSet<double>();
while (k >= 0) if (!h.Add(a[k--])) return false;
return true;
}
Two lines (slow with a repeat ;)
两行（慢速重复；）
static bool repeat(double[] a)
{ return (new HashSet<double>(a).Count < a.Length); }
回答by Basheer AL-MOMANI
take look at my implementation its genericand efficient
看看我的实现它generic和efficient
public static bool HasDuplicates<T>(IList<T> items)
{
Dictionary<T, bool> map = new Dictionary<T, bool>();
for (int i = 0; i < items.Count; i++)
{
if (map.ContainsKey(items[i]))
{
return true; // has duplicates
}
map.Add(items[i], true);
}
return false; // no duplicates
}
here are some calls
这里有一些电话
string[] strings = new[] { "1", "2", "3" };
Utility.HasDuplicates(strings)// this will return false
int[] items=new []{1,2,3,1};
Utility.HasDuplicates(items)// this will return true
回答by Javidan Akberov
We must initialize jfrom ion the first loop and add one(i+1) because we want to compare first loop value with the next value of same array.
我们必须j从i第一个循环开始并添加一个（i+1），因为我们想将第一个循环值与同一数组的下一个值进行比较。
int[] arr = new int[]{1,2,3,1,4,2,5,4};
//create one loop for arr values
for (int i = 0; i < arr.Length; i++)
{
//create nested loop for compare current values with actual value of arr
for (int j = i+1; j < arr.Length; j++)
{
//and here we put our condition
if (arr[i] == arr[j])
{
Console.WriteLine(arr[i]);
}
}
}
回答by Ali Bayat
Generic extension method :
通用扩展方法：
public static bool HasDuplicate<T>(this IEnumerable<T> source, IEqualityComparer<T> comparer)
{
if (source == null)
throw new ArgumentException(nameof(source));
HashSet<T> set = new HashSet<T>(comparer);
foreach (var item in source)
if (!set.Add(item))
return true;
return false;
}
回答by John Tigire
int[] nums = new int[] { 1, 2, 3, 4, 5};
Console.WriteLine(AnyDuplicate(nums));
}
/// <summary>
/// Returns true if there is at least a duplicate in the array.
/// </summary>
/// <returns></returns>
static bool AnyDuplicate(int[] numbers)
{
for (int i = 0; i < numbers.Length; i++)
{
for (int j = i + 1; j < numbers.Length; j++)
{
if (numbers[i] == numbers[j])
{
return true;
}
}
}
return false;
回答by Wesam
use a hashset to add members to, then check if there a previous occurrence of current member
使用散列集添加成员，然后检查是否存在当前成员的先前出现
public bool ContainsDuplicate(double[] nums)
{
int size = nums.Length;
HashSet<double> set1 = new HashSet<double>();
for (int i = 0; i < size; i++)
{
if (set1.Contains(nums[i]))
{
return true;
}
else
{
set1.Add(nums[i]);
}
}
return false;
}
