All possible binary numbers of length n with equal sum in both halves?

CServer Side ProgrammingProgramming

Here we will see all possible binary numbers of n bit (n is given by the user) where the sum of each half is same. For example, if the number is 10001 here 10 and 01 are same because their sum is same, and they are in the different halves. Here we will generate all numbers of that type.

Algorithm

genAllBinEqualSumHalf(n, left, right, diff)

left and right are initially empty, diff is holding difference between left and right

Begin
   if n is 0, then
      if diff is 0, then
         print left + right
      end if
      return
   end if
   if n is 1, then
      if diff is 0, then
         print left + 0 + right
         print left + 1 + right
      end if
      return
   end if
   if 2* |diff| <= n, then
      if left is not blank, then
         genAllBinEqualSumHalf(n-2, left + 0, right + 0, diff)
         genAllBinEqualSumHalf(n-2, left + 0, right + 1, diff-1)
      end if
      genAllBinEqualSumHalf(n-2, left + 1, right + 0, diff + 1)
      genAllBinEqualSumHalf(n-2, left + 1, right + 1, diff)
   end if
End

Example

#include <bits/stdc++.h>
using namespace std;
//left and right strings will be filled up, di will hold the difference between left and right
void genAllBinEqualSumHalf(int n, string left="", string right="", int di=0) {
   if (n == 0) { //when the n is 0
      if (di == 0) //if diff is 0, then concatenate left and right
         cout << left + right << " ";
      return;
   }
   if (n == 1) {//if 1 bit number is their
      if (di == 0) { //when difference is 0, generate two numbers one with 0 after left, another with 1 after left, then add right
         cout << left + "0" + right << " ";
         cout << left + "1" + right << " ";
      }
      return;
   }
   if ((2 * abs(di) <= n)) {
      if (left != ""){ //numbers will not start with 0
         genAllBinEqualSumHalf(n-2, left+"0", right+"0", di);
         //add 0 after left and right
         genAllBinEqualSumHalf(n-2, left+"0", right+"1", di-1);
         //add 0 after left, and 1 after right, so difference is 1 less
      }
      genAllBinEqualSumHalf(n-2, left+"1", right+"0", di+1); //add 1 after left, and 0 after right, so difference is 1 greater
      genAllBinEqualSumHalf(n-2, left+"1", right+"1", di); //add 1 after left and right
   }
}
main() {
   int n = 5;
   genAllBinEqualSumHalf(n);
}

Output

100001
100010
101011
110011
100100
101101
101110
110101
110110
111111
raja
Published on 31-Jul-2019 13:06:08
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