Hello! In this post, we will solve a problem of finding a string using Swift. String problems are common in coding tests, and they greatly help in understanding efficient search algorithms and string processing methods. Through this course, we will solidify our foundation in string processing.<\/p>\n
\nGiven a string haystack<\/code> and needle<\/code>, write a function to find the index of the first occurrence of needle<\/code> in haystack<\/code>. If needle<\/code> does not exist, it should return -1<\/code>.<\/p>\n<\/blockquote>\nExamples:<\/p>\n
\nhaystack = \"hello\"<\/code>, needle = \"ll\"<\/code> => Output: 2<\/code><\/li>\nhaystack = \"aaaaa\"<\/code>, needle = \"bba\"<\/code> => Output: -1<\/code><\/li>\nhaystack = \"\"<\/code>, needle = \"<\/code> => Output: 0<\/code><\/li>\n<\/ul>\nProblem Approach<\/h2>\n
To solve this problem, we need to compare the strings sequentially to check where needle<\/code> appears in haystack<\/code>. We can follow these steps:<\/p>\n\n- First, check the length of
needle<\/code> and compare it with the length of haystack<\/code> to determine if needle<\/code> can exist in haystack<\/code>.<\/li>\n- Then, extract substrings of the length of
needle<\/code> from each index of haystack<\/code> and compare them.<\/li>\n- If the comparison matches, return the index; otherwise, return
-1<\/code>.<\/li>\n<\/ol>\nSwift Code Implementation<\/h2>\n
Now, let’s implement the above logic in Swift:<\/p>\n
func strStr(_ haystack: String, _ needle: String) -> Int {\n let haystackCount = haystack.count\n let needleCount = needle.count\n\n \/\/ Return 0 when needle is empty\n if needleCount == 0 {\n return 0\n }\n\n \/\/ Return -1 if the length of haystack is shorter than needle\n if haystackCount < needleCount {\n return -1\n }\n\n \/\/ Convert haystack to an array\n let haystackArray = Array(haystack)\n\n \/\/ Compare substring with needle at each index\n for i in 0...(haystackCount - needleCount) {\n var j = 0\n\n while j < needleCount && haystackArray[i + j] == needle[needle.index(needle.startIndex, offsetBy: j)] {\n j += 1\n }\n\n \/\/ If needle is found\n if j == needleCount {\n return i\n }\n }\n\n \/\/ If needle is not found\n return -1\n }<\/code><\/pre>\nCode Explanation<\/h2>\n
Now let’s explain the code in detail:<\/p>\n
\nfunc strStr<\/code>: A function that takes two strings haystack<\/code> and needle<\/code> as arguments and performs the string search.<\/li>\nlet haystackCount = haystack.count<\/code>: Stores the length of haystack<\/code>.<\/li>\nlet needleCount = needle.count<\/code>: Stores the length of needle<\/code>.<\/li>\nif needleCount == 0<\/code>: If needle<\/code> is empty, return 0.<\/li>\nif haystackCount < needleCount<\/code>: If the length of haystack<\/code> is shorter than needle<\/code>, return -1 as it cannot be found.<\/li>\nlet haystackArray = Array(haystack)<\/code>: Converts the string into an array to allow access to each character.<\/li>\nfor i in 0...(haystackCount - needleCount)<\/code>: Iterates through all indices of haystack<\/code>. The loop should consider the length of needle<\/code> for the search range.<\/li>\n- The inner
while<\/code> loop compares the substring from needle<\/code> with haystack<\/code> at each index.<\/li>\n- If all comparisons match, it returns index
i<\/code>.<\/li>\n- Finally, it returns -1 if
needle<\/code> is not found.<\/li>\n<\/ul>\nTest Cases<\/h2>\n
Let’s write some test cases to validate this code:<\/p>\n
print(strStr(\"hello\", \"ll\")) \/\/ Output: 2\nprint(strStr(\"aaaaa\", \"bba\")) \/\/ Output: -1\nprint(strStr(\"\", \"\")) \/\/ Output: 0\nprint(strStr(\"abcde\", \"abc\")) \/\/ Output: 0\nprint(strStr(\"abcde\", \"xyz\")) \/\/ Output: -1<\/code><\/pre>\nConclusion<\/h2>\n
In this lesson, we learned how to solve a string finding problem using Swift. It’s important to carefully check the length of the strings, compare substrings, and define the search range to solve the given problem. String-related problems have various variations, so ensure to practice to handle more diverse cases.<\/p>\n
In the next lesson, we will cover another type of string problem. Thank you!<\/p>\n
<\/body><\/p>\n","protected":false},"excerpt":{"rendered":"
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