c# - 如何获取特定字符的索引和重复出现？

Question

如果字符串中有一个或多个字符反复出现。就像在下面的字符串中一样：

1+1+1-2+2/2*4-2*3/23

现在在上面的字符串中，在索引处的出现+次数和在其他索引处的出现次数，然后将它们存储在二维数组中所以现在的问题是如何做到这一点。31,3,7-25,13

Answer 1

以下函数将返回给定搜索字符串的所有匹配索引：

List<int> GetAllIndices(string input, string search)
{
    List<int> result = new List<int>();

    int index = input.IndexOf(search);

    while(index != -1)
    {
        result.Add(index);
        index++;//increment to avoid matching the same index again
        if(index >= input.Length)//check if index is greater than string (causes exception)
            break;
        index = input.IndexOf(search, index);
    }

    return result;
}

它还应该处理重叠匹配，例如：搜索"iii"出现的"ii"将返回[0,1]

---

如果您想使用此函数创建符号列表及其索引，那么我会推荐以下方法：

string input = "1+1+1-2+2/2*4-2*3/23";

//create a dictionary to store the results
Dictionary<string, List<int>> results = new Dictionary<string, List<int>>();

//add results for + symbol
results.Add("+", GetAllIndices(input, "+"));

//add results for - symbol
results.Add("-", GetAllIndices(input, "-"));

//you can then access all indices for a given symbol like so
foreach(int index in results["+"])
{
    //do something with index
}

---

您甚至可以更进一步，将其包装在一个搜索多个符号的函数中：

Dictionary<string, List<int>> GetSymbolMatches(string input, params string[] symbols)
{
    Dictionary<string, List<int>> results = new Dictionary<string, List<int>>();

    foreach(string symbol in symbols)
    {
        results.Add(symbol, GetAllIndices(input, symbol));
    }

    return results;
}

然后您可以像这样使用它：

string input = "1+1+1-2+2/2*4-2*3/23";

Dictionary<string, List<int>> results = GetSymbolMatches(input, "+", "-", "*", "/");

foreach(int index in results["+"])
{
    //do something with index
}

Answer 2

使用 Linq：

var allIndices = yourString.Select((c, i) => new { c, i, })
    .Where(a => a.c == '+').Select(a => a.i);

获取包含字符串中所有字符的字典，例如：

var allCharsAllIndices = yourString.Select((c, i) => new { c, i, })
    .GroupBy(a => a.c)
    .ToDictionary(g => g.Key, g => g.Select(a => a.i).ToArray());

Answer 3

简单=最好。没有内存分配。

public static IEnumerable<int> GetIndexOfEvery(string haystack, string needle)
{
  int index;
  int pos = 0;
  string s = haystack;

  while((index = s.IndexOf(needle)) != -1)
  {              
      yield return index + pos;
      pos = pos + index + 1;
      s = haystack.Substring(pos);
  }
}

Answer 4

你可以通过改变“价值”来尝试这个

var duplicates = param1.ToCharArray().Select((item, index) => new { item, index })
            .Where(x =>x.item==VALUE).GroupBy(g=>g.index)
             .Select(g => new { Key = g.Key  })
            .ToList();

Answer 5

string msg = "1+1+1-2+2/2*4-2*3/23";
Dictionary<char, List<int>> list = new Dictionary<char, List<int>>();
for (int i = 0; i < msg.Length; i++)
{
    if (!list.ContainsKey(msg[i]))
    {
        list.Add(msg[i], new List<int>());
        list[msg[i]].Add(i);
    }
    else
        list[msg[i]].Add(i);
}