Reversals

#include <iostream>
#include <string>

int main(void)
{
  std::ios::sync_with_stdio(0);

  int n, m;
  std::string str;
  std::cin >> n >> m >> str;

  for (int i = 0; i < m; i++) {
    int a = 0, b = 0;
    std::cin >> a >> b;
    a--; b--;

    while (b - a >= 1) {
      char tmp;
      tmp = str[b];
      str[b] = str[a];
      str[a] = tmp;
      a++; b--;
    }
  }

  std::cout << str << std::endl;

  return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: TIME LIMIT EXCEEDED