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
