LeetCode-in-Java
28. Implement strStr()
Easy
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 * 104haystackandneedleconsist of only lower-case English characters.
Solution
public class Solution {
public int strStr(String haystack, String needle) {
if (needle.isEmpty()) {
return 0;
}
int m = haystack.length();
int n = needle.length();
for (int start = 0; start < m - n + 1; start++) {
if (haystack.substring(start, start + n).equals(needle)) {
return start;
}
}
return -1;
}
}