28. Implement strStr()

Implement strStr().

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

Example 3:

Input: haystack = "", needle = ""
Output: 0

Constraints:

• 0 <= haystack.length, needle.length <= 5 * 104
• haystack and needle consist of only lower-case English characters.

# @lc code=start
using LeetCode

function strStr(haystack::String, needle::String)
    needle == "" && return 0
    for i in 1:(length(haystack) - length(needle) + 1)
        if @view(haystack[i:(i + length(needle) - 1)]) == needle
            return i - 1 # Notice that Julia is 1-indexed, and here we need 0-indexed so minus 1
        end
    end
    return -1
end

function strStr2(haystack::AbstractString, needle::AbstractString)

border case

    isempty(needle) && return 0
    length(needle) > length(haystack) && return -1

match needle

    needle == @view(haystack[1:length(needle)]) && return 0

recursive search

    ind = @views strStr2(haystack[2:end], needle)
    return ind == -1 ? -1 : ind + 1
end
# @lc code=end

This page was generated using DemoCards.jl and Literate.jl.