| | | 1 | | // -------------------------------------------------------------------------------- |
| | | 2 | | // Copyright (C) 2025 Eugene Eremeev (also known as Yevhenii Yeriemeieiv). |
| | | 3 | | // All Rights Reserved. |
| | | 4 | | // -------------------------------------------------------------------------------- |
| | | 5 | | // This software is the confidential and proprietary information of Eugene Eremeev |
| | | 6 | | // (also known as Yevhenii Yeriemeieiv) ("Confidential Information"). You shall not |
| | | 7 | | // disclose such Confidential Information and shall use it only in accordance with |
| | | 8 | | // the terms of the license agreement you entered into with Eugene Eremeev (also |
| | | 9 | | // known as Yevhenii Yeriemeieiv). |
| | | 10 | | // -------------------------------------------------------------------------------- |
| | | 11 | | |
| | | 12 | | namespace LeetCode.Algorithms.FindTheIndexOfTheFirstOccurrenceInString; |
| | | 13 | | |
| | | 14 | | /// <inheritdoc /> |
| | | 15 | | public class FindTheIndexOfTheFirstOccurrenceInStringWithKMP : IFindTheIndexOfTheFirstOccurrenceInString |
| | | 16 | | { |
| | | 17 | | /// <summary> |
| | | 18 | | /// Time complexity - O(n + m) |
| | | 19 | | /// Space complexity - O(m) |
| | | 20 | | /// </summary> |
| | | 21 | | /// <param name="haystack"></param> |
| | | 22 | | /// <param name="needle"></param> |
| | | 23 | | /// <returns></returns> |
| | | 24 | | public int StrStr(string haystack, string needle) |
| | 2 | 25 | | { |
| | 2 | 26 | | if (string.IsNullOrEmpty(needle)) |
| | 0 | 27 | | { |
| | 0 | 28 | | return 0; |
| | | 29 | | } |
| | | 30 | | |
| | 2 | 31 | | if (string.IsNullOrEmpty(haystack)) |
| | 0 | 32 | | { |
| | 0 | 33 | | return -1; |
| | | 34 | | } |
| | | 35 | | |
| | 2 | 36 | | var lps = ComputeLongestPrefixSuffixArray(needle); |
| | | 37 | | |
| | 2 | 38 | | var i = 0; |
| | 2 | 39 | | var j = 0; |
| | | 40 | | |
| | 12 | 41 | | while (i < haystack.Length) |
| | 11 | 42 | | { |
| | 11 | 43 | | if (needle[j] == haystack[i]) |
| | 7 | 44 | | { |
| | 7 | 45 | | j++; |
| | 7 | 46 | | i++; |
| | 7 | 47 | | } |
| | | 48 | | |
| | 11 | 49 | | if (j == needle.Length) |
| | 1 | 50 | | { |
| | 1 | 51 | | return i - j; |
| | | 52 | | } |
| | | 53 | | |
| | 10 | 54 | | if (i >= haystack.Length || needle[j] == haystack[i]) |
| | 5 | 55 | | { |
| | 5 | 56 | | continue; |
| | | 57 | | } |
| | | 58 | | |
| | 5 | 59 | | if (j != 0) |
| | 1 | 60 | | { |
| | 1 | 61 | | j = lps[j - 1]; |
| | 1 | 62 | | } |
| | | 63 | | else |
| | 4 | 64 | | { |
| | 4 | 65 | | i += 1; |
| | 4 | 66 | | } |
| | 5 | 67 | | } |
| | | 68 | | |
| | 1 | 69 | | return -1; |
| | 2 | 70 | | } |
| | | 71 | | |
| | | 72 | | private static int[] ComputeLongestPrefixSuffixArray(string needle) |
| | 2 | 73 | | { |
| | 2 | 74 | | var length = needle.Length; |
| | 2 | 75 | | var lps = new int[length]; |
| | | 76 | | |
| | 2 | 77 | | lps[0] = 0; |
| | | 78 | | |
| | 2 | 79 | | var len = 0; |
| | 2 | 80 | | var i = 1; |
| | | 81 | | |
| | 8 | 82 | | while (i < length) |
| | 6 | 83 | | { |
| | 6 | 84 | | if (needle[i] == needle[len]) |
| | 0 | 85 | | { |
| | 0 | 86 | | len++; |
| | 0 | 87 | | lps[i] = len; |
| | 0 | 88 | | i++; |
| | 0 | 89 | | } |
| | | 90 | | else |
| | 6 | 91 | | { |
| | 6 | 92 | | if (len == 0) |
| | 6 | 93 | | { |
| | 6 | 94 | | lps[i] = len; |
| | 6 | 95 | | i++; |
| | 6 | 96 | | } |
| | | 97 | | else |
| | 0 | 98 | | { |
| | 0 | 99 | | len = lps[len - 1]; |
| | 0 | 100 | | } |
| | 6 | 101 | | } |
| | 6 | 102 | | } |
| | | 103 | | |
| | 2 | 104 | | return lps; |
| | 2 | 105 | | } |
| | | 106 | | } |