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String Search algorithm
This code might be a bit confusion when without explanation. Please visit my homepage for the algorithm explanation: http://www.algoonline.net/String_Search_algorithm/string_search_algorithm.htm Put a thumb up thanks.
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‎String_search_3.txt

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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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namespace String_Search
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{
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class Program
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{
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struct P_Bad_Character_struct
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{
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public char P_Char;
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public int Bad_Character_Shift;
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public P_Bad_Character_struct(char input1, int input2)
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{
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P_Char = input1;
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Bad_Character_Shift = input2;
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}
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}
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static void Main(string[] args)
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{
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//string T = "GTTATAGCTGATCGCGGCGTAGCGGCGATAT"; //original
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//string T = "GTTATAGCTGATCCCGGCGTAGCGGCGATATCTCCCCC";
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//string T = "GTTAGAGCTGATCGCGGCGTAGCGGCGATATCGAGCGGCGCCTCATAGTAGATA";
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string T = "TGCATGTTAGAGTGATGAAGCGATAAAAGGTAGGTAGCGGCGTAGGAAAACCGTGATAGTAGAAAAATATAGATAAGATACGCAATTACA"; //
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//string T = "CGTGCCTACTTACTTACTTACTTACGCGAA"; //
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//string P = "CTTACTTAC";
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//string P = "GTAGCGGCG"; //original
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//string T = "GTTATAGCTGATCGCGGCGTAGCGGCGAA"; //original
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//string P = "GTTA";
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//string P = "CGTAG";
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//string P = "GCGG";
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//string P = "CGTA";
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//string P = "GCGA";
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//string P = "TGATCGC";
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//string P = "GCGATAT";
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//string P = "ATAGTAGATA";
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//string P = "TAGATAAGATA";
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//string P = "AAA";
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//string P = "CGCAATTACA"; //10 characters
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//string P = "CC";
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//string P = "A";
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//string P = "TC";
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//string P = "CCTC";
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//string P = "CTCCCCC";
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//string P = "ATC";
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//string P = "AAAA";
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string P = "AAAAA";
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int P_position_in_T = string_search(P, T);
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if (P_position_in_T == -1)
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Console.WriteLine("P string not exist in string T");
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else //P_position_in_T >= 0
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Console.WriteLine("String P is found inside string T, between " + P_position_in_T + " to " + (P_position_in_T + P.Length - 1));
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Console.Read();
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}
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private static int string_search(string P, string T)
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{
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string matched_string = "";
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int start_P_in_T = 0;
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int end_P_in_T = P.Length - 1;
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int T_ptr;
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//Check string 'P' & 'T' are not empty and T string is longer than P string, or else definitely will not be any matches and no reason to proceed the checking
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if (!String.IsNullOrEmpty(P) && !String.IsNullOrEmpty(T) && T.Length >= P.Length)
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{
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if (P.Length == 1) //Special case: if string 'P' only consist of 1 character
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{
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T_ptr = 0;
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while (T_ptr < T.Length && P[0] != T[T_ptr])
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T_ptr++;
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if (T_ptr != T.Length)
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return T_ptr;
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else
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return -1;
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}
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int P_ptr; //Pointer showing position of target search string 'P' last character now
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T_ptr = P.Length - 1; //Pointer showing position of target search string 'P' last character in string 'T' now
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//To optimize quick shifting, contruct string 'P' number of shift array table
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//First case: when only last character of string 'P' matching string 'T', how many characters shift string 'P' should be in string 'T'
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P_ptr = P.Length - 2;
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int only_last_character_of_P_matching_shift;
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while (P_ptr >= 0 && P[P_ptr] != P.Last())
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P_ptr--;
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only_last_character_of_P_matching_shift = P.Length - 1 - P_ptr;
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//Second case: when string 'P' suffix partially matching string 'T', 2 characters & more. How many characters shift string 'P' should be in string 'T'
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matched_string = P.Substring(P.Length - 2, 2);
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int matched_string_ptr = 1;
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//P_ptr pointer continue from only_last_character_of_P_matching case
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int[] P_Good_Suffix_shift_table = new int[P.Length - 2];
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//P_Good_Suffix_Rule
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finding_good_suffix_shift:
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if (P_ptr >= 0)
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{
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finding_good_suffix_shift_2:
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if (matched_string[matched_string_ptr] == P[P_ptr])
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{
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if (P_ptr == 0 || matched_string_ptr == 0)
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goto found_good_suffix_shift;
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matched_string_ptr--;
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}
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else
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{
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if (matched_string_ptr != matched_string.Count() - 1)
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{
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matched_string_ptr = matched_string.Count() - 1;
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goto finding_good_suffix_shift_2;
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}
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}
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P_ptr--;
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goto finding_good_suffix_shift;
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}
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found_good_suffix_shift:
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if (P_ptr > 0) //Match string are found in the mid of remaining P string
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{
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P_Good_Suffix_shift_table[matched_string.Length - 2] = P.Length - matched_string.Length - P_ptr;
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P_ptr--;
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//matched_string increase length by 1
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matched_string = P.Substring(P.Length - matched_string.Length - 1, matched_string.Length + 1); //matched_string increase length by 1
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matched_string_ptr = 0; //search suffix from previous shorter suffix position, 1 character to the left
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goto finding_good_suffix_shift; //should goto finding_good_suffix_shift_2
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}
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else if (P_ptr == 0) //Match string are found in the start of remaining P string
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{
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int P_Good_Suffix_shift = P.Length - matched_string.Count() + matched_string_ptr;
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for (int i = matched_string.Length - 2; i < P.Length - 2; i++)
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P_Good_Suffix_shift_table[i] = P_Good_Suffix_shift;
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//goto P_Bad_Character_Rule;
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}
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else //When P_ptr < 0, no match found in remaining P string
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{
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for (int i = matched_string.Length - 2; i < P.Length - 2; i++)
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P_Good_Suffix_shift_table[i] = P.Length;
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//goto P_Bad_Character_Rule;
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}
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//Third case: when string 'P' last character does not match string 'T'
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//P_Bad_Character_Rule
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P_ptr = P.Length - 2;
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List<P_Bad_Character_struct> P_Bad_Character_shift_table = new List<P_Bad_Character_struct>();
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while (P_ptr >= 0 && P[P_ptr] == P.Last())
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P_ptr--;
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//P_ptr == -1, special case when string 'P' only consist of only one duplicated character
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if (P_ptr != -1) //string 'P' has character different from P.Last()
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{
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P_Bad_Character_shift_table.Add(new P_Bad_Character_struct(P[P_ptr], P.Length - 1 - P_ptr)); //Add P second last character into the table
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P_ptr--;
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while (P_ptr >= 0) //when string P.length >= 3
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{
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int i = 0;
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while (i < P_Bad_Character_shift_table.Count() && P_Bad_Character_shift_table[i].P_Char != P[P_ptr])
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i++;
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if (i == P_Bad_Character_shift_table.Count() && P[P_ptr] != P.Last()) //P current character not occur inside P_Bad_Character_shift_table, add this new character & it position
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P_Bad_Character_shift_table.Add(new P_Bad_Character_struct(P[P_ptr], P.Length - 1 - P_ptr));
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P_ptr--;
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}
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for (int i = 0; i < P_Bad_Character_shift_table.Count(); i++)
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Console.WriteLine("P_Bad_Character_shift_table.P_Char[" + i + "] = " + P_Bad_Character_shift_table[i].P_Char
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+ ", Bad_Character_Shift = " + P_Bad_Character_shift_table[i].Bad_Character_Shift);
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for (int i = 0; i < P_Good_Suffix_shift_table.Count(); i++)
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Console.WriteLine("P_Good_Suffix_shift_table[" + i + "] = " + P_Good_Suffix_shift_table[i]);
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}
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//Start string 'P' against string 'T' comparison
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int matched_string_length = 0;
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P_ptr = P.Length - 1;
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string_compare_P_against_T:
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if (T_ptr < T.Length)
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{
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//String compare from string 'P' last character toward first character against string 'T'. Stop whenever there is a mismatch.
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while (P_ptr >= 0 && P[P_ptr] == T[T_ptr])
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{
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matched_string_length++;
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T_ptr--;
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P_ptr--;
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}
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if (matched_string_length == 0) //Bad Character Rule
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{
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if (P_Bad_Character_shift_table.Count() == 0)
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{
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//special case when string 'P' only consist of only one duplicated character
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start_P_in_T += P.Length;
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end_P_in_T += P.Length;
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}
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else
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{
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int i = 0;
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while (i < P_Bad_Character_shift_table.Count() && P_Bad_Character_shift_table[i].P_Char != T[end_P_in_T])
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i++;
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if (i == P_Bad_Character_shift_table.Count())
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{
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//string 'T' character correspond to string 'P' last character position cannot be found in string 'P'
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start_P_in_T += P.Length;
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end_P_in_T += P.Length;
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}
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else
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{
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start_P_in_T += P_Bad_Character_shift_table[i].Bad_Character_Shift;
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end_P_in_T += P_Bad_Character_shift_table[i].Bad_Character_Shift;
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}
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}
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Console.Write("Bad Character Rule, ");
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}
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else if (matched_string_length == 1)
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{
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//Only P last character match
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start_P_in_T += only_last_character_of_P_matching_shift;
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end_P_in_T += only_last_character_of_P_matching_shift;
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Console.Write("Only P last character match, ");
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}
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else if (matched_string_length == P.Length) //found string 'P' matching string 'T' in this position
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return start_P_in_T; //return the position of string 'P' in string 'T'
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else //P against T matched string is 2 characters or more but not exactly matched, only partially match
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{
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//Good Suffix Rule
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start_P_in_T += P_Good_Suffix_shift_table[matched_string_length - 2];
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end_P_in_T += P_Good_Suffix_shift_table[matched_string_length - 2];
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Console.Write("Good Suffix Rule, ");
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}
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T_ptr = end_P_in_T;
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P_ptr = P.Length - 1;
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matched_string_length = 0;
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Console.WriteLine("start_P_in_T = " + start_P_in_T);
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goto string_compare_P_against_T;
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}
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}
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return -1; //found string 'P' not matching string 'T'
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}
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}
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}

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