28. Implement strStr()

Problem:

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 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().

思路：

利用string的substr()方法即可。

Solution (C++):

int strStr(string haystack, string needle) {
    if (needle == "")  return 0;
    int n = haystack.length(), m = needle.length();
    
    for (int i = 0; i <= n - m; ++i) {
        if (haystack.substr(i, m) == needle)
            return i;
    }
    return -1;
}

性能：

Runtime: 4 ms  Memory Usage: 6.9 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB