28. Implement strStr()

题目：

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
解题思路：
brute-force 复杂度为O(MN)。下次有机会写一个O(n)的KMP

class Solution(object):
def strStr(self, haystack, needle):
"""
:type haystack: str
:type needle: str
:rtype: int
"""
if len(needle)==0:return 0
for i,c in enumerate(haystack):
tmp = haystack[i:i+len(needle)]
if tmp==needle:return i
return -1

class Solution {
public:
int strStr(string haystack, string needle) {
int n = haystack.size();
int m = needle.size();
if(m==0)return 0;
for(int i=0;i<=n-m;i++)
{
string tmp = haystack.substr(i,m);
if(tmp==needle)return i;
}
return -1;
}
};