String Without AAA or BBB in C++

Suppose we have two integers A and B, we have to return any string S, such that −

• S has length A + B and contains exactly A number of letter ‘a’ and B number of ‘b’ letters.

• Substring “aaa” and “bbb” will not be in the string S

So if the given integers are A = 4, B = 1, then the result will be “aabaa”.

To solve this, we will follow these steps −

• Define a string ret, initially this is empty

• while |A – B| >= 2,

  • if A > B, then

    • ret := ret concatenate ‘aa’

    • decrease A by 2

    • if B is non-zero concatenate ‘b’ with ret and decrease B by 1

  • else

    • ret := ret concatenate ‘bb’

    • decrease B by 2

    • if A is non-zero concatenate ‘a’ with ret and decrease A by 1

• while either A is non-zero, or B is non-zero

  • if A is non zero and (size of ret < 2 or not of (size of ret >= 2 and last element of ret = second last element of ret) and last element of ret is ‘a’), then

    • ret := ret + ‘a’, decrease A by 1

    • if B is non-zero

      • ret := ret concatenate ‘b’, decrease B by 1

    • otherwise ret concatenate ‘b’, decrease B by 1, if A is not 0, then concatenate a with ret and decrease A by 1

• return ret

Let us see the following implementation to get better understanding −

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
   public:
   string strWithout3a3b(int A, int B) {
      string ret = "";
      while(abs(A - B) >= 2){
         if(A > B){
            ret += 'a';
            ret += 'a';
            A -= 2;
            if(B) {
               ret += 'b';
               B--;
            }
         }else{
            ret += 'b';
            ret += 'b';
              B -= 2;
              if(A) {
               ret += 'a';
               A--;
            }
         }  
     }
      while(A || B){
         if(A && (ret.size() < 2 || !(ret.size() >= 2 && ret[ret.size() - 1] == ret[ret.size() -                2] && ret[ret.size() - 1] == 'a') ) ){
            ret += 'a';
            A--;
            if(B) {
               ret += 'b';
               B--;
            }
         }else{
            ret += 'b';
            B--;
            if(A) {
              ret += 'a';
              A--;
            }
         }      
      }
      return ret;
   }
};
main(){
   Solution ob;
   cout << (ob.strWithout3a3b(4, 1));
}

Input

4
1

Output

"aabaa"