Implement StrStr ()

Implement strStr ().

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

Example 1:

Input:haystack = "Hello", needle = "ll" Output:2

Example 2:

Input:haystack = "AAAAA", needle = "BBA" Output: 1

Clarification:

What's should we return when was an needle empty string? This was a great question to ask during a interview.

For the purpose of this problem, we'll return 0 when was an needle empty string. This is consistent to C ' s strstr () and Java's IndexOf ().

AC Code:

This code is a low effective.

Class Solution {public:    int strStr (String haystack, string needle) {        int len1 = Haystack.length ();        int len2 = Needle.length ();        if (Len2 = = 0) {            return 0;        }        for (int i = 0; i < len1; ++i) {            int index = i;            int j = 0;            while (haystack[index] = = Needle[j] && Index < len1 && J < len2) {                index++;                j + +;            }            if (j = = Len2) {                return i;            }        }        return-1;    }};

Runtime: 812 MS, faster than 3.41% of C + + online submissions for Implement strStr ().

Only there is a little change, but the effective has a big exaltation.

Class Solution {public:    int strStr (String haystack, string needle) {        int len1 = Haystack.length ();        int len2 = Needle.length ();        if (Len2 = = 0) {            return 0;        }
I < len1-len2 for         (int i = 0; i < len1-len2+1; ++i) {            int index = i;            int j = 0;            while (haystack[index] = = Needle[j] && Index < len1 && J < len2) {                index++;                j + +;            }            if (j = = Len2) {                return i;            }        }        return-1;    }};

Runtime: 8 ms, faster than 37.69% of C + + online submissions for Implement strStr ().

It is a brute-force algorithm, too. May is this question want the use Brute-force.

The high effective algorithm are to use KMP algorithm.

Class Solution {Public:int strStr (String haystack, string needle) {int m = haystack.length (), n = needle.lengt        H ();        if (!n) {return 0;        } vector<int> lps = kmpprocess (needle); for (int i = 0, j = 0; i < m;)                {if (haystack[i] = = Needle[j]) {i++;            j + +;            } if (j = = N) {return i-j; if ((I < m) && (haystack[i]! = Needle[j])) {if (j) {j = Lps[j                -1];                } else {i++;    }}} return-1;        }private:vector<int> kmpprocess (string& needle) {int n = needle.length ();        Vector<int> LPs (n, 0); for (int i = 1, len = 0; i < n;)            {if (needle[i] = = Needle[len]) {lps[i++] = ++len; } else if (len) {len = lps[len-1];           } else {lps[i++] = 0;    }} return LPs; }};

Runtime: 8 ms, faster than 37.69% of C + + online submissions for Implement strStr ().

Implement StrStr ()