28. Implement strStr()

class Solution {
public:
    int strStr(string haystack, string needle) {
        int m = haystack.length()   ,   n = needle.length();
        
        if(n==0)    return 0;   //if needle is empty
        
        for(int i=0; i<=m-n; i++){
            if(haystack[i]==needle[0] && haystack[i+n-1]==needle[n-1]){     //comparing first and lasts element of same size string array startinng from i
                for(int j=0;j<n;j++){
                    if(haystack[i+j]!=needle[j])
                        break;          //break and go to next index if any charachter in between does not match
                    if(j==n-1)
                        return i;       //if needle reaches its end therefore it is fully processed
                }
                    
            }
        }
    return -1;
    }
};
/*
Runtime: 8 ms, faster than 85.27% of C++ online submissions for Implement strStr().
Memory Usage: 7.1 MB, less than 66.31% of C++ online submissions for Implement strStr().
*/