长度为n的所有可能的二进制数，两半相等

给定一个数字n，我们需要打印出所有n位二进制数，并且左右半部分的总和相等。如果n为奇数，则mid元素可以为0或1。

例子：

Input  : n = 4
Output : 0000 0101 0110 1001 1010 1111 
Input : n = 5
Output : 00000 00100 01001 01101 01010 01110 10001 10101 10010 10110 11011 11111 

这样做的想法是递归地建立左右两半，并跟踪其中的1计数之间的差异。当差变为0并且没有更多字符可添加时，我们将打印一个字符串。

C++

// C++ program to generate all binary strings with
// equal sums in left and right halves.
#include 
using namespace std;
  
/* Default values are used only in initial call.
   n is number of bits remaining to be filled
   di is current difference between sums of
      left and right halves.
   left and right are current half substrings. */
void equal(int n, string left="", string right="",
                                        int di=0)
{
    // TWO BASE CASES
    // If there are no more characters to add (n is 0)
    if (n == 0)
    {
        // If difference between counts of 1s and
        // 0s is 0 (di is 0)
        if (di == 0)
            cout << left + right << " ";
        return;
    }
  
    /* If 1 remains than string length was odd */
    if (n == 1)
    {
        // If difference is 0, we can put remaining
        // bit in middle.
        if (di == 0)
        {
            cout << left + "0" + right << " ";
            cout << left + "1" + right << " ";
        }
        return;
    }
  
    /* If difference is more than what can be
       be covered with remaining n digits
       (Note that lengths of left and right
        must be same) */
    if ((2 * abs(di) <= n))
    {  
          
         /* add 0 to end in both left and right
         half. Sum in both half will not
               change*/
         equal(n-2, left+"0", right+"0", di);
  
         /* add 0 to end in both left and right
         half* subtract 1 from di as right
         sum is increased by 1*/
         equal(n-2, left+"0", right+"1", di-1);
  
        /* add 1  in end in left half and 0 to the
        right half. Add 1 to di as left sum is
        increased by 1*/
        equal(n-2, left+"1", right+"0", di+1);
  
        /* add 1 in end to both left and right
          half the sum will not change*/
        equal(n-2, left+"1", right+"1", di);
    }
}
  
/* driver function */
int main()
{
    int n = 5; // n-bits
    equal(n);
    return 0;
}

Java

// Java program to generate all binary strings 
// with equal sums in left and right halves.
import java.util.*;
  
class GFG
{
  
// Default values are used only in initial call.
// n is number of bits remaining to be filled
// di is current difference between sums of
// left and right halves.
// left and right are current half substrings. 
static void equal(int n, String left, 
                         String right, int di)
{
    // TWO BASE CASES
    // If there are no more characters to add (n is 0)
    if (n == 0)
    {
        // If difference between counts of 1s and
        // 0s is 0 (di is 0)
        if (di == 0)
            System.out.print(left + right + " ");
        return;
    }
  
    /* If 1 remains than string length was odd */
    if (n == 1)
    {
        // If difference is 0, we can put 
        // remaining bit in middle.
        if (di == 0)
        {
            System.out.print(left + "0" + right + " ");
            System.out.print(left + "1" + right + " ");
        }
        return;
    }
  
    /* If difference is more than what can be
    be covered with remaining n digits
    (Note that lengths of left and right
     must be same) */
    if ((2 * Math.abs(di) <= n))
    {
          
            // add 0 to end in both left and right
            // half. Sum in both half will not
            // change
            equal(n - 2, left + "0", right + "0", di);
  
            // add 0 to end in both left and right
            // half* subtract 1 from di as right
            // sum is increased by 1
            equal(n - 2, left + "0", right + "1", di - 1);
          
  
        // add 1 in end in left half and 0 to the
        // right half. Add 1 to di as left sum is
        // increased by 1*
        equal(n - 2, left + "1", right + "0", di + 1);
  
        // add 1 in end to both left and right
        // half the sum will not change
        equal(n - 2, left + "1", right + "1", di);
    }
}
  
// Driver Code
public static void main(String args[])
{
    int n = 5; 
      
    // n-bits
    equal(n, "", "", 0);
}
}
  
// This code is contributed 
// by SURENDRA_GANGWAR

Python3

# Python program to generate all binary strings with
# equal sums in left and right halves.
  
# Default values are used only in initial call.
# n is number of bits remaining to be filled
# di is current difference between sums of
# left and right halves.
# left and right are current half substrings.
def equal(n: int, left = "", right = "", di = 0):
  
    # TWO BASE CASES
    # If there are no more characters to add (n is 0)
    if n == 0:
  
        # If difference between counts of 1s and
        # 0s is 0 (di is 0)
        if di == 0:
            print(left + right, end = " ")
        return
  
    # If 1 remains than string length was odd
    if n == 1:
  
        # If difference is 0, we can put remaining
        # bit in middle.
        if di == 0:
            print(left + "0" + right, end = " ")
            print(left + "1" + right, end = " ")
        return
  
    # If difference is more than what can be
    # be covered with remaining n digits
    # (Note that lengths of left and right
    # must be same)
    if 2 * abs(di) <= n:
       
        # add 0 to end in both left and right
        # half. Sum in both half will not
        # change
        equal(n - 2, left + "0", right + "0", di)
  
        # add 0 to end in both left and right
        # half* subtract 1 from di as right
        # sum is increased by 1
        equal(n - 2, left + "0", right + "1", di - 1)
  
        # add 1 in end in left half and 0 to the
        # right half. Add 1 to di as left sum is
        # increased by 1
        equal(n - 2, left + "1", right + "0", di + 1)
  
        # add 1 in end to both left and right
        # half the sum will not change
        equal(n - 2, left + "1", right + "1", di)
  
# Driver Code
if __name__ == "__main__":
    n = 5 # n-bits
    equal(5)
  
# This code is contributed by
# sanjeev2552

C#

// C# program to generate all binary strings 
// with equal sums in left and right halves.
using System;
  
class GFG
{
  
// Default values are used only in initial call.
// n is number of bits remaining to be filled
// di is current difference between sums of
// left and right halves.
// left and right are current half substrings. 
static void equal(int n, String left, 
                         String right, int di)
{
    // TWO BASE CASES
    // If there are no more characters
    // to add (n is 0)
    if (n == 0)
    {
        // If difference between counts of 1s 
        // and 0s is 0 (di is 0)
        if (di == 0)
            Console.Write(left + right + " ");
        return;
    }
  
    /* If 1 remains than string length was odd */
    if (n == 1)
    {
        // If difference is 0, we can put 
        // remaining bit in middle.
        if (di == 0)
        {
            Console.Write(left + "0" + 
                          right + " ");
            Console.Write(left + "1" + 
                          right + " ");
        }
        return;
    }
  
    /* If difference is more than what can be
    be covered with remaining n digits
    (Note that lengths of left and right
    must be same) */
    if ((2 * Math.Abs(di) <= n))
    {
  
          
            // add 0 to end in both left and right
            // half. Sum in both half will not
            // change
            equal(n - 2, left + "0", right + "0", di);
  
            // add 0 to end in both left and right
            // half* subtract 1 from di as right
            // sum is increased by 1
            equal(n - 2, left + "0", 
                  right + "1", di - 1);
          
  
        // add 1 in end in left half and 0 to the
        // right half. Add 1 to di as left sum is
        // increased by 1*
        equal(n - 2, left + "1", 
              right + "0", di + 1);
  
        // add 1 in end to both left and right
        // half the sum will not change
        equal(n - 2, left + "1", right + "1", di);
    }
}
  
// Driver Code
public static void Main(String []args)
{
    int n = 5; 
      
    // n-bits
    equal(n, "", "", 0);
}
}
  
// This code is contributed by 29AjayKumar

输出：

10001 10101 10010 10110 11011 11111