1 public class Solution 2     { 3  4         public string[] Permute(string S) 5         { 6             List
     
      
       > dic = new List
       
        
         >(); 7             int baseindex = 0; 8             var temp = S; 9             var mask = "";10             while (temp.IndexOf('{
    ') >= 0)11             {12                 int begin = temp.IndexOf('{
    ');13                 int end = temp.IndexOf('}');14                 var ary = new List
         
          ();15                 for (int i = begin + 1; i < end; i++)16                 {17                     if (temp[i] != ',')18                     {19                         ary.Add(temp[i]);20                     }21                 }22                 dic.Add(ary);23                 mask = mask + temp.Substring(0, begin) + "#";24                 baseindex = end + 1;25                 temp = temp.Substring(baseindex);26             }27             mask += S.Substring(S.LastIndexOf('}') + 1);28 29             var result = LetterCombinations(S, mask, dic);30             return result.OrderBy(x => x).ToArray();31         }32 33         public IList
          
            LetterCombinations(string S, string mask, List
           
            
             > dic)34 {35 var combinations = new List
             
              ();36 37 if (string.IsNullOrEmpty(S))38 return combinations;39 40 combinations.Add("");41 foreach (var digits in dic)42 {43 var next = new List
              
               ();44 45 foreach (char letter in digits)46 {47 foreach (string combo in combinations)48 {49 var dstr = combo + letter;50 next.Add(dstr);51 }52 }53 combinations = next;54 }55 56 for (int i = 0; i < combinations.Count; i++)57 {58 var cur = combinations[i];59 for (var j = 0; j < mask.Length; j++)60 {61 if (mask[j] != '#')62 {63 cur = cur.Insert(j, mask[j].ToString());64 }65 }66 combinations[i] = cur;67 }68 69 return combinations;70 }71 }
              
             
            
           
          
         
        
       
      
     

 

思路分析：将字符串的"{}"内的部分和常规字符分开处理。对于大括号内的部分，先将括号内的字符进行“组合”，然后再把常规字符插入到相应的位置。

本题的主要思想和是一样的。