How to implement the strStr() function in LeetCode problem 28?

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pythondef implement_strstr(haystack, needle): if needle==: return 0 for i in range(len(haystack) - len(needle) + 1): if haystack[i:i+len(needle)]==needle: return i return -1

Example 1print(implement_strstr(hello, ll))

Example 2print(implement_strstr(aaaaa, bba))

ImplementstrStr().

Return the index of the first occurrence of needle in haystack, or-1if 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()​​.

题解：

很多测试用例没说清楚

class Solution {
public:
int strStr(string haystack, string needle) {
if (needle.size() == 0) {
return 0;
}
if (haystack.size() < needle.size()) {
return -1;
}
int res = -1;
for (int i = 0; i <= haystack.size() - needle.size(); i++) {
int k = i;
for (int j = 0; j < needle.size(); j++) {
if (haystack[k] != needle[j]) {
break;
}
else {
k++;
}
if (j == needle.size() - 1) {
if (res == -1) {
res = i;
}
else {
res = min(res, i);
}
}
}
}
return res;
}
};