remove the duplicate(重复) characters from a string

/*Design  an  algorithm  and  write  code  to  remove  the  duplicate(重复)  characters  in  a string without using any additional buffer.  NOTE: One or two additional variablesare fine.An extra copy of the array is not */#include <iostream>#include <string>using namespace std;void removeDuplicates(string &str){int len = str.length();if(len < 2)return;//new_end为无重复元素数组末元素下一位置的下标int new_end = 1;for (int i = 1;i < len;++i){int j;//判断str[0...new_end-1]和str[i...len-1]是否有相等元素for (j = 0;j < new_end;++j){//str[i]与str[0...new_end-1]中元素相等，则跳出for循环，接着判断str[i+1]if (str[j] == str[i])break;//str[i]不与str[0...new_end-1]中元素相等，则令str[new_end]等于str[i]}if(j == new_end){str[new_end] = str[i];++new_end;}}str[new_end] = '\0';}void print_c_str(string str)  {  for (int i = 0;i < str.length();++i){if(str.at(i) == '\0')break;cout << str[i];}cout << endl;}int main(){string s1 = "";string s2 = "aaaa";string s3 = "aaaabbbb";string s4 = "abababab";removeDuplicates(s1);removeDuplicates(s2);removeDuplicates(s3);removeDuplicates(s4);print_c_str(s1);print_c_str(s2);print_c_str(s3);print_c_str(s4);return 0;}