Problem p01811 (C++) — buggy submission, verdict: Memory Limit Exceeded

#include <algorithm>
#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <string>
#include <vector>
//    #include <boost/multiprecision/cpp_int.hpp>
#include <functional>
#define int long long
#define inf 1000000007
#define pa pair<int, int>
#define ll long long
#define pal pair<double, pa>
#define ppa pair<pa, int>
#define ppap pair<int, pa>
#define ssa pair<string, int>
#define mp make_pair
#define pb push_back
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;
// priority_queue<int, vector<int>, greater<int> > que;
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double a) { return Point(x * a, y * a); }
  Point operator/(double a) { return Point(x / a, y / a); }
  double absv() { return sqrt(norm()); }
  double norm() { return x * x + y * y; }
  bool operator<(const Point &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;

struct Segment {
  Point p1, p2;
};

double hen(Vector a) {
  if (fabs(a.x) < EPS && a.y > 0)
    return acos(0);
  else if (fabs(a.x) < EPS && a.y < 0)
    return 3 * acos(0);
  else if (fabs(a.y) < EPS && a.x < 0)
    return 2 * acos(0);
  else if (fabs(a.y) < EPS && a.x > 0)
    return 0.0;
  else if (a.y > 0)
    return acos(a.x / a.absv());
  else
    return 2 * acos(0) + acos(-a.x / a.absv());
}

string itos(int i) {
  ostringstream s;
  s << i;
  return s.str();
}

int gcd(int v, int b) {
  if (v > b)
    return gcd(b, v);
  if (v == b)
    return b;
  if (b % v == 0)
    return v;
  return gcd(v, b % v);
}
double dot(Vector a, Vector b) { return a.x * b.x + a.y * b.y; }
double cross(Vector a, Vector b) { return a.x * b.y - a.y * b.x; }

double distans(double x1, double y1, double x2, double y2) {
  double rr = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
  return sqrt(rr);
}
/*}
int pr[100010];
//int inv[100010];

int beki(int wa,int rr){
if(rr==0) return 1ll;
if(rr==1) return wa;
if(rr%2==1) return (beki(wa,rr-1)*wa)%inf;
int zx=beki(wa,rr/2);
return (zx*zx)%inf;
}

void gya(){
pr[0]=1;
for(int i=1;i<100010;i++){
pr[i]=(pr[i-1]*i)%inf;
}
for(int i=0;i<100010;i++) inv[i]=beki(pr[i],inf-2);

}

*/

//----------------kokomade tenpure------------
bool b = false;

void ch(string s) {
  // cout<<s<<endl;
  if (b)
    return;
  if (s == "ABC") {
    b = true;
    return;
  }
  if (s.length() <= 4)
    return;

  int l = s.length();
  vector<int> ve;
  int z[3] = {0};
  for (int i = 0; i < l; i++) {
    if (s.substr(i, 3) == "ABC") {
      ve.pb(i);
      //	cout<<i<<endl;
      i += 2;
    } else {
      z[s[i] - 'A']++;
    }
  }
  if (ve.size() == 0)
    return;
  for (int i = 0; i < 3; i++) {
    string st = s;
    string xc = "A";
    xc[0] += i;
    if (z[i] > 0)
      continue;
    for (int j = ve.size() - 1; j >= 0; j--) {
      string s2 = st.substr(ve[j] + 3);
      //		cout<<s2<<endl;
      st = st.substr(0, ve[j]) + xc + s2;
    }
    ch(st);
  }

  return;
}

signed main() {
  string s;
  cin >> s;
  ch(s);
  if (b)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
  /*
  while(1){
          cin>>n>>m;
          if(n==0&&m==0) return 0;


  }
  */

  return 0;
}

Error: MLE

Fixed submission:

#include <algorithm>
#include <bits/stdc++.h>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <string>
#include <vector>
//    #include <boost/multiprecision/cpp_int.hpp>
#include <functional>
#define int long long
#define inf 1000000007
#define pa pair<int, int>
#define ll long long
#define pal pair<double, pa>
#define ppa pair<pa, int>
#define ppap pair<int, pa>
#define ssa pair<string, int>
#define mp make_pair
#define pb push_back
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;
// priority_queue<int, vector<int>, greater<int> > que;
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double a) { return Point(x * a, y * a); }
  Point operator/(double a) { return Point(x / a, y / a); }
  double absv() { return sqrt(norm()); }
  double norm() { return x * x + y * y; }
  bool operator<(const Point &p) const { return x != p.x ? x < p.x : y < p.y; }
  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;

struct Segment {
  Point p1, p2;
};

double hen(Vector a) {
  if (fabs(a.x) < EPS && a.y > 0)
    return acos(0);
  else if (fabs(a.x) < EPS && a.y < 0)
    return 3 * acos(0);
  else if (fabs(a.y) < EPS && a.x < 0)
    return 2 * acos(0);
  else if (fabs(a.y) < EPS && a.x > 0)
    return 0.0;
  else if (a.y > 0)
    return acos(a.x / a.absv());
  else
    return 2 * acos(0) + acos(-a.x / a.absv());
}

string itos(int i) {
  ostringstream s;
  s << i;
  return s.str();
}

int gcd(int v, int b) {
  if (v > b)
    return gcd(b, v);
  if (v == b)
    return b;
  if (b % v == 0)
    return v;
  return gcd(v, b % v);
}
double dot(Vector a, Vector b) { return a.x * b.x + a.y * b.y; }
double cross(Vector a, Vector b) { return a.x * b.y - a.y * b.x; }

double distans(double x1, double y1, double x2, double y2) {
  double rr = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
  return sqrt(rr);
}
/*}
int pr[100010];
//int inv[100010];

int beki(int wa,int rr){
if(rr==0) return 1ll;
if(rr==1) return wa;
if(rr%2==1) return (beki(wa,rr-1)*wa)%inf;
int zx=beki(wa,rr/2);
return (zx*zx)%inf;
}

void gya(){
pr[0]=1;
for(int i=1;i<100010;i++){
pr[i]=(pr[i-1]*i)%inf;
}
for(int i=0;i<100010;i++) inv[i]=beki(pr[i],inf-2);

}

*/

//----------------kokomade tenpure------------
bool b = false;

void ch(string s) {
  // cout<<s<<endl;
  if (b)
    return;
  if (s == "ABC") {
    b = true;
    return;
  }
  if (s.length() <= 4)
    return;

  int l = s.length();
  vector<int> ve;
  int z[3] = {0};
  for (int i = 0; i < l; i++) {
    if (s.substr(i, 3) == "ABC") {
      ve.pb(i);
      //	cout<<i<<endl;
      i += 2;
    } else {
      z[s[i] - 'A']++;
    }
  }

  for (int i = 0; i < 3; i++) {
    string st = s;
    string xc = "A";
    xc[0] += i;
    if (z[i] > 0)
      continue;
    for (int j = ve.size() - 1; j >= 0; j--) {
      string s2 = st.substr(ve[j] + 3);
      //		cout<<s2<<endl;
      st = st.substr(0, ve[j]) + xc + s2;
    }
    ch(st);
  }

  return;
}

signed main() {
  string s;
  cin >> s;
  ch(s);
  if (b)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
  /*
  while(1){
          cin>>n>>m;
          if(n==0&&m==0) return 0;


  }
  */

  return 0;
}