MLE / SEGF error

I learn by doing, and enjoy using online judge sites to learn. Right now I am working on http://www.z-training.net/tasks.php?show_task=5000000406. Some of the test cases pass, but many get MLE/SEGF. My code is taking a brute force approach. Is this approach the cause of the MLE/SEGF error?

//z-last char
#include <iostream>
#include <string>
using namespace 开发者_StackOverflow社区std;

int main()
{
string str = "";
string tmp = "";
  string newStr = "";
  unsigned int strSize = 0;
  unsigned int repeat;
  unsigned int i;
  int cnt = 0;

  cin >> str;
  cin >> repeat;

  tmp = str;
  strSize = str.size();

  for (i=1;i<repeat;i++)
  {
    str += tmp;
    strSize += strSize;
  }

  while (strSize > 1)
  {
    cnt = 0;
    newStr = "";
    for (i=1;i<strSize;i=i+2)
    {
      newStr += str[i];
      cnt += 1;
    }
    //cout << newStr << endl;
    strSize = cnt;
    str = newStr;

  }

  cout << newStr << endl;
  return 0;
}

---

I see a few problems here. In C and C++, arrays are numbered starting at 0 and end at allocated length - 1.

str[0] refers to the first character in str.
str[str.length() - 1] refers to the last character in a str.

Also, C strings are terminated with a binary 0. Some C++ string libraries keep their strings in C library format so the C string functions can be used on them. If you're disturbing the 0 at the end of the strings and the string library is trying to use a C string lib function that can also cause seg faults.

You're likely getting seg faults because you're reading or writing memory out of bounds.