题目描述
Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example1:
Input: haystack = "hello", needle = "ll" Output: 2
Example2:
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().
class Solution {
public:
int strStr(string haystack, string needle) {
if(needle.size() == 0){
return 0;
}
int n = haystack.size();
int m = needle.size();
for(int i = 0; i <= n - m; i++){
int j = 0;
for(; j < m; j++){
if(haystack[i + j] != needle[j]){
break;
}
}
if(j == m){
return i; // 如果最后匹配成功，那么肯定是从i开始匹配的，我们只需要返回i即可
}
}
return -1;
}
};
