Implement strStr()
Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba"
Output: -1
Clarification:
What should we return whenneedle
is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 whenneedle
is an empty string. This is consistent to C's strstr() and Java's indexOf().
Solution
class Solution {
// "aaaaa", "b" => -1
// "aaaaa", "a" => 0
// "aa", "aa" => 0
// hello, ll => 2
public int strStr(String haystack, String needle) {
int index = -1;
if (needle == null || haystack == null) {
return index;
}
if (needle.length() > haystack.length()) {
return index;
}
if (needle.equals(haystack)) {
return 0;
}
for (int i = 0; i < haystack.length(); i++) {
if (i + needle.length() <= haystack.length()) {
// for example: hello & ll
// 2 + 2 <= 5, try to compare substring(2, 2 + 2) == needle
if (haystack.substring(i, i + needle.length()).equals(needle)) {
return i;
}
}
}
return index;
}
}
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