[Swift] Implement strStr()

Implement strStr.

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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().

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Constraints:

• 1 <= haystack.length, needle.length <= $10^4$
• haystack and needle consist of only lowercase English characters.

풀러가기

문제 이해

코드

class Solution {
  func strStr(_ haystack: String, _ needle: String) -> Int {
    var strIndex = 0
    var haystack = haystack
    while 0 <= haystack.count - needle.count {
      if haystack.hasPrefix(needle) {
        return strIndex
      }
      haystack.removeFirst()
      
      strIndex += 1
    }
    
    return -1
  }
}

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