[Swift]LeetCode28. 实现strStr() | Implement strStr()
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Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll" Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba" Output: -1
Clarification:
What should we return when needle is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().
实现 strStr() 函数。
给定一个 haystack 字符串和一个 needle 字符串，在 haystack 字符串中找出 needle 字符串出现的第一个位置 (从0开始)。如果不存在，则返回 -1。
示例 1:
输入: haystack = "hello", needle = "ll" 输出: 2
示例 2:
输入: haystack = "aaaaa", needle = "bba" 输出: -1
说明:
当 needle 是空字符串时，我们应当返回什么值呢？这是一个在面试中很好的问题。
对于本题而言，当 needle 是空字符串时我们应当返回 0 。这与C语言的 strstr() 以及 Java的 indexOf() 定义相符。
12ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 let count1 = haystack.count 4 let count2 = needle.count 5 if count2 == 0 { 6 return 0 7 } 8 9 if count1 < count2 { 10 return -1 11 } 12 13 var haystackChars = haystack.cString(using: .utf8)! 14 var needleChars = needle.cString(using: .utf8)! 15 var i = 0 16 var j = 0 17 18 let maxi = count1 - count2 19 let maxj = count2 - 1 20 21 while i <= maxi && j <= maxj { 22 var m = i 23 while m <= count1 - 1 && j <= maxj { 24 let mv = haystackChars[m] 25 let jv = needleChars[j] 26 if mv == jv { 27 m += 1 28 j += 1 29 continue 30 } 31 j = 0 32 i += 1 33 break 34 } 35 } 36 j = j - 1 37 if j == maxj{ 38 return i 39 } 40 41 return -1 42 } 43 }
16ms
1 class Solution { 2 3 func strStr(_ haystack: String, _ needle: String) -> Int { 4 guard needle.count != 0 && !haystack.hasPrefix(needle) else{ 5 return 0 6 } 7 guard haystack.count != needle.count else { 8 return -1 9 } 10 guard haystack.contains(needle) else { 11 return -1 12 } 13 14 var stop = false 15 var low = 0 16 var high = haystack.count 17 18 while !stop { 19 let start = haystack.index(haystack.startIndex, offsetBy: low) 20 let end = haystack.index(haystack.endIndex, offsetBy: high-haystack.count) 21 let range = Range<String.Index>(uncheckedBounds: (lower: start, upper: end)) 22 23 let str = String(haystack[range]) 24 25 if str.count <= needle.count*3 { 26 if str.hasPrefix(needle) { 27 stop = true 28 return low 29 }else { 30 low += 1 31 } 32 }else { 33 let middle = str.count/2 34 let prefixStr = str.prefix(middle + needle.count) 35 if prefixStr.contains(needle) { 36 if str.hasPrefix(needle) { 37 stop = true 38 return low 39 } 40 high -= middle 41 high += needle.count 42 }else { 43 low += middle 44 low -= needle.count 45 } 46 } 47 } 48 } 49 }
20ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 guard !needle.isEmpty else { 4 return 0 5 } 6 let sCount = haystack.count, pCount = needle.count 7 guard sCount >= pCount else { 8 return -1 9 } 10 let s = Array(haystack), p = Array(needle) 11 var i = 0, j = 0 12 while i < s.count && j < p.count { 13 if s[i] == p[j] { 14 i += 1 15 j += 1 16 } else { 17 i = i - j + 1 18 j = 0 19 } 20 } 21 return j == pCount ? i - j : -1 22 } 23 }
24ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 if needle.count == 0 { 4 return 0 5 } 6 7 if haystack.count == 0 { 8 return -1 9 } 10 11 var search = haystack[haystack.startIndex..<haystack.endIndex] 12 while search.count > 0 { 13 if let first = search.firstIndex(of: needle.first!), let endindex = search.index(first, offsetBy: needle.count, limitedBy: search.endIndex) { 14 let match = search[first..<endindex] 15 if match == needle { 16 return haystack.distance(from: haystack.startIndex, to: first) 17 } 18 19 if first != search.endIndex { 20 if let b = search.index(first, offsetBy: 1, limitedBy: search.endIndex) { 21 search = search[b..<search.endIndex] 22 } 23 } 24 } else { 25 break 26 } 27 } 28 29 return -1 30 } 31 }
28ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 let sCount = haystack.count, pCount = needle.count 4 guard pCount > 0 && sCount >= pCount else { 5 return pCount == 0 ? 0 : -1 6 } 7 let p = Array(needle) 8 //为了提高效率，用空间换时间，初始化一个字典记录p中每个字符最后出现的位置 9 var charDictionary = [Character: Int]() 10 for index in stride(from: pCount - 1, through: 0, by: -1) { 11 let char = p[index] 12 if charDictionary[char] == nil { 13 charDictionary[char] = index 14 } 15 } 16 let s = Array(haystack) 17 var i = 0, j = 0 18 while i < sCount && j < pCount { 19 if s[i] == p[j] { 20 i += 1 21 j += 1 22 } else { 23 let nextSCharIndex = i + (pCount - 1 - j) + 1 24 if nextSCharIndex < sCount { 25 let nextSChar = s[nextSCharIndex] 26 if let index = charDictionary[nextSChar] { 27 i = i - j + pCount - 1 - index + 1 28 } else { 29 i = i - j + pCount + 1 30 } 31 j = 0 32 } else { 33 break 34 } 35 } 36 } 37 return j == pCount ? i - j : -1 38 } 39 }
32ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 guard !needle.isEmpty else { 4 return 0 5 } 6 let sCount = haystack.count, pCount = needle.count 7 guard sCount >= pCount else { 8 return -1 9 } 10 let s = Array(haystack), p = Array(needle) 11 var next = Array(repeating: -1, count: pCount) 12 var k = -1, j = 0 13 while j < pCount - 1 { 14 if k == -1 || p[j] == p[k] { 15 j += 1 16 k += 1 17 if p[j] != p[k] { 18 next[j] = k 19 } else { 20 next[j] = next[k] 21 } 22 } else { 23 k = next[k] 24 } 25 } 26 var i = 0 27 j = 0 28 while i < s.count && j < p.count { 29 if j == -1 || s[i] == p[j] { 30 i += 1 31 j += 1 32 } else { 33 j = next[j] 34 } 35 } 36 return j == pCount ? i - j : -1 37 } 38 }
44ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 //当 needle 是空字符串时应当返回 0 4 if needle.isEmpty{return 0} 5 //获取字符的长度 6 let haystackLen = haystack.count 7 let needleLen = needle.count 8 //haystack字符串字符长度小于needle字符串，则返回-1 9 if haystackLen < needleLen{return -1} 10 //needle的第一个字符 11 let firstChar = needle[needle.startIndex] 12 //遍历haystack字符串,讲Int转化为String.Index 13 for i in 0...haystackLen-needleLen 14 { 15 //截取字符串的开始处索引 16 let firstIndex = haystack.index(haystack.startIndex, offsetBy: i) 17 //截取字符串的结束处索引 18 let endIndex = haystack.index(haystack.startIndex, offsetBy: i + needleLen) 19 //截取字符串，注意要用String.Index的方式访问字符串 20 let subStr = haystack[firstIndex..<endIndex] 21 //判断截取的字符串是否等于needle 22 if subStr == needle 23 { 24 //返回索引 25 return i 26 } 27 } 28 //没有匹配，返回-1 29 return -1 30 } 31 }
52ms
1 class Solution { 2 func strStr(_ haystack: String, _ needle: String) -> Int { 3 guard !needle.isEmpty else { return 0 } 4 guard needle.count <= haystack.count else { return -1 } 5 for i in 0...(haystack.count-needle.count) { 6 let substr = String(Array(haystack)[i..<(i+needle.count)]) 7 if substr == needle { 8 return i 9 } 10 } 11 return -1 12 } 13 }
