/*

StrStr:

strStr My Submissions

19% Accepted

strstr (a.k.a find sub string), is a useful function in string operation. You task is to implement this function.

For a given source string and a target string, you should output the "first" index(from 0) of target string in source string.

If target is not exist in source, just return -1.

Example

If source="source" and target="target", return -1.

If source="abcdabcdefg" and target="bcd", return 1.

Challenge

O(n) time.

Clarification

Do I need to implement KMP Algorithm in an interview?

- Not necessary. When this problem occurs in an interview, the interviewer just want to test your basic implementation ability.

Tags Expand

Basic Implementation String

Thinking process:

Two Pointer.

String Null case.

Break Statement.

Check position i+j of source and position j of target. If not match, break out.

If j matches target.length(), means target is fully embedded in source.

return start point of target in source: i

*/

public int strStr(String source, String target) {

//Check Null

if(source == null || target == null){

return -1;

}

//Two Pointer check for target

int i,j;

for (i = 0; i < source.length() - target.length() + 1; i++){

for (j = 0; j < target.length(); j++){

if (source.charAt(i+j) != target.charAt(j)){

break;

}

}

if( j == target.length()){

return i;

}

}

//'target' not found:

return -1;

}