Using Binary Search with Vectors.

问题

I'm trying to implement an algorithm that for each string in the first vector it does a binary search in the second vector and will output "YES:" if it finds a match or "No:" otherwise.

Right now with my program my algo always outputs "NO:" and I can't find out what's going wrong. Any hints or tips would be appreciated.

My Binary search:

bool binary_search(const vector<string>& sorted_vec, string key) {
size_t mid, left = 0 ;
size_t right = sorted_vec.size(); // one position passed the right end
while (left < right) {
    mid = left + (right - left)/2;
    if (key > sorted_vec[mid]){
        left = mid+1;
   } else if (key < sorted_vec[mid]){                                        
        right = mid;
   } else {                                                                  
        return true;

            }                                                                
        return false;                                                        
    }
}

My Algo:

if(algo_speed == "fast"){

    string key = fileContent[i];

    while(getline(ifs1, line)){

            fileContent1.push_back(line);

    }

    sort(fileContent1.begin(), fileContent1.end());
    for(size_t i = 0; i < fileContent.size(); i++){
    string temp = fileContent[i];
    bool found = binary_search(fileContent1,temp) ;

     if(found == true) {
            cout << "YES:" << fileContent.at(i) << endl;
        } else {
            cout << "NO:" << fileContent.at(i) << endl;
        }
    }

}

回答1:

You are exiting your function on the first miss with the misplaced return false:

bool binary_search(const vector<string>& sorted_vec, string key) {
   size_t mid, left = 0 ;
   size_t right = sorted_vec.size(); // one position passed the right end
   while (left < right) {
      mid = left + (right - left)/2;
      if (key > sorted_vec[mid]){
          left = mid+1;
      }
      else if (key < sorted_vec[mid]){                                        
        right = mid;
      }
      else {                                                                  
        return true;
     }                                                                                                               
   }

   return false;      
}

来源：https://stackoverflow.com/questions/18774858/using-binary-search-with-vectors

标签

c++

algorithm

vector

binary