implement-strstr.cpp

//question//


Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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().

 

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1
Example 3:

Input: haystack = "", needle = ""
Output: 0
 

Constraints:

0 <= haystack.length, needle.length <= 5 * 104
haystack and needle consist of only lower-case English characters.




//solution//


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