28.ImplementStrStr.md

28. Implement strStr()

Description

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.

Solution

• java

/*
 Success Detail:
 Runtime: 0 ms, faster than 100.00% of Java online submissions for Implement strStr().
 Memory Usage: 36.8 MB, less than 93.44% of Java online submissions for Implement strStr().
 */
class Solution {
    public int strStr(String haystack, String needle) {
        if ("".equals(needle)) return 0;
        int haystackLen = haystack.length();
        int needleLen = needle.length();

        for (int i = 0; i <= haystackLen - needleLen; i++) {
            if (haystack.startsWith(needle, i)) {
                return i;
            }
        }
        return -1;
    }
}