algorithm - C++: Implementing merge sort from scratch -


i trying test self , wanted write mergesort, without looking code online, , in time period. stuck @ point cannot understand doing wrong, since merge sort, as remember, divide strings point string 1 character , later on merge them together. code i've written below tries exact thing. wondering whether got concept wrong, or my implementation?

string merge(string str1, string str2) {   string final = "";   int = 0, j = 0;   bool fromstr1 = false;    while(true) {     if(str1[i] < str2[j]) {       final += str1[i];       i++;       if(i == str1.size()) {         break;       }     }     else {       final += str2[j];       j++;       if(j == str2.size()) {         break;         fromstr1 = true;       }     }   }    if(fromstr1) {     for(int t = i; t < str1.size(); t++) {       final += str1[t];     }   }   else {     for(int t = j; t < str2.size(); t++) {       final += str2[t];     }   }    return final; }  string mergesort(string str1, int start, int end) {   if(end - start == 1)     return str1;   else {     int pivot = (end - start) / 2;     string newstr1 = mergesort(str1, start, pivot);     string newstr2 = mergesort(str1, pivot + 1, end);     return merge(newstr1, newstr2);   } }

note changes:

#include <iostream> #include <string>  using namespace std;  string merge(string str1, string str2) {   string final = "";   int = 0, j = 0;   bool fromstr1 = false;    while (true) {     if (i >= (int)str1.size()) {       break;     }     if (j >= (int)str2.size()) {       fromstr1 = true; // changed order of break!       break;     }      if (str1[i] < str2[j]) {       final += str1[i];       i++;     }     else {       final += str2[j];       j++;     }   }    if (fromstr1) {     (int t = i; t < (int)str1.size(); t++) {       final += str1[t];     }   }   else {     for(int t = j; t < (int)str2.size(); t++) {       final += str2[t];     }   }    return final; }  string mergesort(string str1) {   int len = str1.size();   if (len <= 1)     return str1;   else {     string newstr1 = mergesort(str1.substr(0, len / 2));     string newstr2 = mergesort(str1.substr(len / 2, len - len / 2));     return merge(newstr1, newstr2);   } }  int main() {   cout << '"' << mergesort("") << '"' << endl;   cout << '"' << mergesort("a") << '"' << endl;   cout << '"' << mergesort("ba") << '"' << endl;   cout << '"' << mergesort("132") << '"' << endl;   cout << '"' << mergesort("4321") << '"' << endl;   cout << '"' << mergesort("54321") << '"' << endl;   return 0; }

output (ideone):

"" "a" "ab" "123" "1234" "12345"

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