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[leetcode] problem 28 – implement strstr()

admin 11月 13, 2020 0

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example

No.1

Input: haystack = “hello”, needle = “ll”

Output: 2

No.2

Input: haystack = “aaaaa”, needle = “bba”

Output: -1

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().

Code

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public int (String haystack, String needle) {
    for (int i = 0; i <= haystack.length() - needle.length(); i++) {
        for (int j = 0; ; j++) {
            if (j == needle.length())
                return i;

            if (needle.charAt(j) != haystack.charAt(i+j))
                break;
        }
    }

    return -1;
}
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