85 Determine If One String Is Another's Substring (Lai)

Determine if a small string is a substring of another large string.

Return the index of the first occurrence of the small string in the large string.

Return -1 if the small string is not a substring of the large string.

Assumptions

• Both large and small are not null
• If small is empty string, return 0

Examples

• “ab” is a substring of “bcabc”, return 2
• “bcd” is not a substring of “bcabc”, return -1
• "" is substring of "abc", return 0