433. Minimum Genetic Mutation

MinMutation.cs

public class Solution {
  public int MinMutation(string start, string end, string[] bank) {
    var q = new Queue<string>();
    var visited = new HashSet<string>();
    var minMutation = 0;

    q.Enqueue(start);
    
    while(q.Count > 0){
      var sz = q.Count;
      while(sz > 0){
        var currentGen = q.Dequeue();
        if(currentGen == end)
          return minMutation;
        
        foreach(var bankGen in bank){
          if(visited.Contains(bankGen) || EditDistance(currentGen, bankGen) != 1)
            continue;
          q.Enqueue(bankGen);
          visited.Add(bankGen);
        }
        sz--;
      }
      
      minMutation++;
    }

    return -1;
  }

  private static int EditDistance(in string s1, in string s2){
    var distance = 0;
    for(var i = 0; i < s1.Length; ++i){
      if(s1[i] != s2[i])
        distance++;
    }
    return distance;
  }
}