LintCode(easy)字符串查找

class Solution {
public:
    /**
     * 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.
     */
  int strStr(const char *source, const char *target) {
        if(!target||!source) return -1;
        string A(source); int m; 
    string B(target);  vector<int> v1;
    // 截取字符串前三个字符

    if (A.size() < B.size()) return -1;
    else{
        if (B.size() > 3){
            for (int i = 0; i < A.size(); i++){
                if (A[i] == B[0] && A[i + 1] == B[1] && A[i + 2] == B[2])
                v1.push_back(i + 3);

            }
            if (v1.size() == 0) return -1;
            for (auto c : v1){
                for (m = 0; m < B.size()-3; m++)
                if (A[c+m] != B[3+m])   break;          
                if (m == B.size()-3) 
                    return c - 3;
            }

        }
        else{
            for (int i = 0; i < A.size() - B.size() + 2; i++){
                for (m = 0; m < B.size() ; m++)
                    if (A[i+m] != B[m]) break;
                if (m == B.size())
                    return i+m - B.size(); 
            }
        }
    }   return -1;

     }



};