Problem p00017 (C++) — buggy submission, verdict: Time Limit Exceeded

// include
//------------------------------------------
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}

// math
//-------------------------------------------
template <class T> inline T sqr(T x) { return x * x; }

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

// container util
//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())

// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)

// constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);

// clear memory
#define CLR(a) memset((a), 0, sizeof(a))

// debug
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

int gcd(int a, int b) {
  int tmp;
  while (a % b == 0) {
    tmp = a % b;
    a = b;
    b = tmp;
  }
}

int lcm(int a, int b) { return a * b / gcd(a, b); }

bool prime_number(int n) {
  if (n < 2) {
    return false;
  } else if (n == 2) {
    return true;
  }
  if (n % 2 == 0) {
    return false;
  }
  for (int i = 3; i <= n / i; i += 2) {
    if (n % i == 0)
      return false;
    return true;
  }
}

int main() {
  string a;

  while (getline(cin, a)) {
    while (a.find("the") == string::npos && a.find("this") == string::npos &&
           a.find("that") == string::npos)
      REP(i, a.size()) {
        if (a[i] == 'z')
          a[i] = 'a';
        else if (a[i] >= 'a' && a[i] <= 'z')
          a[i]++;
      }
    cout << a << endl;
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <iostream>
#include <iterator>
#include <string>
using namespace std;

int main() {

  string str;
  bool ans = false;

  while (getline(cin, str)) {
    ans = false;

    string::iterator ite = str.begin();

    while (1) {
      // cout << str.find("the");
      if (str.find("the") <= str.size())
        ans = true;
      else if (str.find("this") <= str.size())
        ans = true;
      else if (str.find("that") <= str.size())
        ans = true;
      if (ans)
        break;
      for (int i = 0; i < str.size(); i++) {
        if (*(ite + i) >= 'A' && *(ite + i) <= 'z')
          *(ite + i) -= 1;
      }
    }
    cout << str << endl;
  }
  return 0;
}