28.implement strstr

刷题内容

• https://leetcode.com/problems/implement-strstr/

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().


˼· **- ʱ�临�Ӷ�: O(N)*- �ռ临�Ӷ�: O(1)***

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class Solution {
public:
int strStr(string haystack, string needle) {
int j = 0,i = 0,index= 0;
while(i < haystack.size() && j < needle.size())
{
if(haystack[i] == needle[j])
{
if(!j)
index = i;
j++;
i++;
}
else
{
i = ++index;
j = 0;
}
}
if(j == needle.size())
return index;
return -1;
}
};


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