Implement strStr()

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.

Solutions

🧠 Cpp

class Solution
{
public:
    int strStr(string haystack, string needle)
    {
        if(haystack == needle || needle.empty())
            return 0;

        for(auto iter = begin(haystack);
            iter < end(haystack);
            ++iter)
        {
            if(end(haystack) - iter < needle.size())
                return -1;

            if(*iter == needle.front())
            {
                bool are_same = false;
                //check is chunk the same
                for(auto iter_A = iter, iter_B = begin(needle);
                    iter_A < end(haystack) && iter_B < end(needle);
                    ++iter_A, ++ iter_B
                    )
                    if(*iter_A != *iter_B)
                        break;
                    else if(next(iter_B) == end(needle))
                        are_same = true;

                    if(are_same)
                        return iter - begin(haystack);
            }
        }

        return -1;
    }
};