Problem p03788 (C++)

Buggy submission (status: Time Limit Exceeded):
// by yjz
#include <bits/stdc++.h>
using namespace std;
#define FF first
#define SS second
#define PB push_back
#define MP make_pair
#define bged(v) (v).begin(), (v).end()
#define foreach(it, s)                                                         \
  for (__typeof((s).begin()) it = (s).begin(); it != (s).end(); it++)
typedef long long ll;
const int Imx = 2147483647;
const ll Lbig = 2e18;
const int mod = 1e9 + 7;
// My i/o stream
struct fastio {
  char s[100000];
  int it, len;
  fastio() { it = len = 0; }
  inline char get() {
    if (it < len)
      return s[it++];
    it = 0;
    len = fread(s, 1, 100000, stdin);
    if (len == 0)
      return EOF;
    else
      return s[it++];
  }
  bool notend() {
    char c = get();
    while (c == ' ' || c == '\n')
      c = get();
    if (it > 0)
      it--;
    return c != EOF;
  }
} _buff;
#define geti(x) x = getnum()
#define getii(x, y) geti(x), geti(y)
#define getiii(x, y, z) getii(x, y), geti(z)
#define puti(x) putnum(x), putchar(' ')
#define putii(x, y) puti(x), puti(y)
#define putiii(x, y, z) putii(x, y), puti(z)
#define putsi(x) putnum(x), putchar('\n')
#define putsii(x, y) puti(x), putsi(y)
#define putsiii(x, y, z) putii(x, y), putsi(z)
inline ll getnum() {
  ll r = 0;
  bool ng = 0;
  char c;
  c = _buff.get();
  while (c != '-' && (c < '0' || c > '9'))
    c = _buff.get();
  if (c == '-')
    ng = 1, c = _buff.get();
  while (c >= '0' && c <= '9')
    r = r * 10 + c - '0', c = _buff.get();
  return ng ? -r : r;
}
template <class T> inline void putnum(T x) {
  if (x < 0)
    putchar('-'), x = -x;
  register short a[20] = {}, sz = 0;
  while (x)
    a[sz++] = x % 10, x /= 10;
  if (sz == 0)
    putchar('0');
  for (int i = sz - 1; i >= 0; i--)
    putchar('0' + a[i]);
}
inline char getreal() {
  char c = _buff.get();
  while (c == ' ' || c == '\n')
    c = _buff.get();
  return c;
}
int n, k;
char s[200111];
char getst(int x, int dlt) {
  if (x + dlt > n)
    return (n - x) % 2 + 'A';
  else
    return ((s[x + dlt] - 'A') ^ (dlt % 2)) + 'A';
}
char ans[200111];
int main() {
  scanf("%d%d", &n, &k);
  scanf("%s", s + 1);
  int dlt = 0;
  bool f = 0;
  while (k--) {
    if (dlt >= n)
      k %= 2;
    if (((getst(1, dlt) - 'A') ^ f) == 0) {
      f ^= 1;
    } else {
      dlt++;
      f = 0;
    }
    for (int i = 1; i <= n; i++)
      ans[i] = getst(i, dlt);
    /*		if(f)
                    {
                            ans[1]=((ans[1]-'A')^1)+'A';
                    }
                    printf("%s\n",ans+1);*/
  }
  for (int i = 1; i <= n; i++)
    ans[i] = getst(i, dlt);
  if (f) {
    ans[1] = ((ans[1] - 'A') ^ 1) + 'A';
  }
  printf("%s\n", ans + 1);
  return 0;
}

Fixed submission:
// by yjz
#include <bits/stdc++.h>
using namespace std;
#define FF first
#define SS second
#define PB push_back
#define MP make_pair
#define bged(v) (v).begin(), (v).end()
#define foreach(it, s)                                                         \
  for (__typeof((s).begin()) it = (s).begin(); it != (s).end(); it++)
typedef long long ll;
const int Imx = 2147483647;
const ll Lbig = 2e18;
const int mod = 1e9 + 7;
// My i/o stream
struct fastio {
  char s[100000];
  int it, len;
  fastio() { it = len = 0; }
  inline char get() {
    if (it < len)
      return s[it++];
    it = 0;
    len = fread(s, 1, 100000, stdin);
    if (len == 0)
      return EOF;
    else
      return s[it++];
  }
  bool notend() {
    char c = get();
    while (c == ' ' || c == '\n')
      c = get();
    if (it > 0)
      it--;
    return c != EOF;
  }
} _buff;
#define geti(x) x = getnum()
#define getii(x, y) geti(x), geti(y)
#define getiii(x, y, z) getii(x, y), geti(z)
#define puti(x) putnum(x), putchar(' ')
#define putii(x, y) puti(x), puti(y)
#define putiii(x, y, z) putii(x, y), puti(z)
#define putsi(x) putnum(x), putchar('\n')
#define putsii(x, y) puti(x), putsi(y)
#define putsiii(x, y, z) putii(x, y), putsi(z)
inline ll getnum() {
  ll r = 0;
  bool ng = 0;
  char c;
  c = _buff.get();
  while (c != '-' && (c < '0' || c > '9'))
    c = _buff.get();
  if (c == '-')
    ng = 1, c = _buff.get();
  while (c >= '0' && c <= '9')
    r = r * 10 + c - '0', c = _buff.get();
  return ng ? -r : r;
}
template <class T> inline void putnum(T x) {
  if (x < 0)
    putchar('-'), x = -x;
  register short a[20] = {}, sz = 0;
  while (x)
    a[sz++] = x % 10, x /= 10;
  if (sz == 0)
    putchar('0');
  for (int i = sz - 1; i >= 0; i--)
    putchar('0' + a[i]);
}
inline char getreal() {
  char c = _buff.get();
  while (c == ' ' || c == '\n')
    c = _buff.get();
  return c;
}
int n, k;
char s[200111];
char getst(int x, int dlt) {
  if (x + dlt > n)
    return (n - x) % 2 + 'A';
  else
    return ((s[x + dlt] - 'A') ^ (dlt % 2)) + 'A';
}
char ans[200111];
int main() {
  scanf("%d%d", &n, &k);
  scanf("%s", s + 1);
  int dlt = 0;
  bool f = 0;
  while (k--) {
    if (dlt >= n)
      k %= 2;
    if (((getst(1, dlt) - 'A') ^ f) == 0) {
      f ^= 1;
    } else {
      dlt++;
      f = 0;
    }
    /*		for(int i=1;i<=n;i++)ans[i]=getst(i,dlt);
                    if(f)
                    {
                            ans[1]=((ans[1]-'A')^1)+'A';
                    }
                    printf("%s\n",ans+1);*/
  }
  for (int i = 1; i <= n; i++)
    ans[i] = getst(i, dlt);
  if (f) {
    ans[1] = ((ans[1] - 'A') ^ 1) + 'A';
  }
  printf("%s\n", ans + 1);
  return 0;
}