text: Fill two instances of all numbers from 1 to n in a specific way | A backtracking based C Program to fill two instances of all numbers from 1 to n in a specific way ; A recursive utility function to fill two instances of numbers from 1 to n in res [ 0. .2 n - 1 ] . ' curr ' is current value of n . ; If current number becomes 0 , then all numbers are filled ; Try placing two instances of ' curr ' at all possible locations till solution is found ; Two ' curr ' should be placed at ' curr + 1' distance ; Plave two instances of ' curr ' ; Recur to check if the above placement leads to a solution ; If solution is not possible , then backtrack ; This function prints the result for input number ' n ' using fillUtil ( ) ; Create an array of size 2 n and initialize all elements in it as 0 ; If solution is possible , then print it . ; Driver program
code: #include <stdio.h> NEW_LINE #include <stdbool.h> NEW_LINE bool fillUtil ( int res [ ] , int curr , int n ) { if ( curr == 0 ) return true ; int i ; for ( i = 0 ; i < 2 * n - curr - 1 ; i ++ ) { if ( res [ i ] == 0 && res [ i + curr + 1 ] == 0 ) { res [ i ] = res [ i + curr + 1 ] = curr ; if ( fillUtil ( res , curr - 1 , n ) ) return true ; res [ i ] = res [ i + curr + 1 ] = 0 ; } } return false ; } void fill ( int n ) { int res [ 2 * n ] , i ; for ( i = 0 ; i < 2 * n ; i ++ ) res [ i ] = 0 ; if ( fillUtil ( res , n , n ) ) { for ( i = 0 ; i < 2 * n ; i ++ ) printf ( " % d ▁ " , res [ i ] ) ; } else puts ( " Not ▁ Possible " ) ; } int main ( ) { fill ( 7 ) ; return 0 ; }