[刷题]strStr

[LIntCode]strStr

class Solution {
    /**
     * Returns a index to the first occurrence of target in source,
     * or -1  if target is not part of source.
     * @param source string to be scanned.
     * @param target string containing the sequence of characters to match.
     */
    public int strStr(String source, String target) {
        //2015-4-20
        if (source == null || target == null) {
            return -1;
        }
        if (target.length() == 0) {
            return 0;
        }
        if (source.length() == 0) {
            return -1;
        }
        if (source.length() < target.length()) {
            return -1;
        }
        
        for (int i = 0; i <= source.length() - target.length() ; i++) {
            int k = 0;
            for (int j = 0; j < target.length(); j++) {
                if (source.charAt(i + k) != target.charAt(j)) {
                    break;
                }
                k++;
            }
            if (k == target.length()) {
                return i;
            }
        }
        return -1;
    }
}