Check if a string can be made by chars of another string in C#

Question

How to check, if a word can be made by letters of another word. using every letter only once.

Example:

if str = "computer"; then

//if user enters below words output must be true
  comp
  put
  poet

//and if user enters below words output must be false
  count         // since n is not in str 
  root          // since there is only single o in str    

Answer 1

This is a solution based on counting the number of each character and then checking that the second word has fewer of each character:

public static bool UsesSameLetters(string input, string check)
{
    var OriginalCounts = input.GroupBy(c => c)
        .ToDictionary(g => g.Key, g => g.Count());
    bool Success = check.GroupBy(c => c)
        .All(originalCounts.ContainsKey(g.Key) 
            && originalCounts[g.Key] >= g.Count);
    return Success;
}

This solution counts the number of each character in the input string, and then checks if every character in the check string occurs less times than it does in the input string. This solution is fairly declaritive.

Answer 2

The following should do the trick

public static bool UsesSameLetters(string input, string check) {
  var array = new BitArray(check.Length, false);
  for (var i = 0; i < input.Length; i++) {   
    var found = false;
    for (var j = 0; j < check.Length; j++) {
      if (input[i] == check[j] && !array.Get(j)) {
        array.Set(j, true);
        found = true;
        break;
      }
    }
    if (!found) {
      return false;
    }
  }
  return true;
}