28. Find the Index of the First Occurrence in a String

Hint

class Solution {
public:
    int strStr(string haystack, string needle)
    {
        // Iterate through 'haystack' from the start to the point where 'needle' can fit
        for ()
        {
            // Iterate through each character in 'needle'
            for ()
            {
                // If the characters don't match, break out of the inner loop

                // If we reach the end of 'needle' and all characters have matched
                if ()
                {
                    // Return the starting index of the first occurrence of 'needle' in 'haystack'
                }
            }
        }
        // If 'needle' is not found in 'haystack', return -1
    }
};

class Solution {
public:
    int strStr(string haystack, string needle)
    {
        for (int i = 0; i <= haystack.size() - needle.size(); ++i)
        {
            for (int j = 0; j < needle.size(); ++j)
            {
                if (needle[j] != haystack[i + j]) break;
                if (j == needle.size() - 1)
                {
                    return i;
                }
            }
        }
        return -1;
    }
};

• T: $O(n * m)$
• S: $O(1)$