Length of the smallest number which is divisible by K and formed by using 1 's only | Function to return length of the resultant number ; If K is a multiple of 2 or 5 ; Instead of generating all possible numbers 1 , 11 , 111 , 111 , ... , K 1 's  Take remainder with K ; If number is divisible by k then remainder will be 0 ; Driver code
function numLen ( K ) { if ( K % 2 == 0 K % 5 == 0 ) return - 1 ; var number = 0 ; var len = 1 ; for ( len = 1 ; len <= K ; len ++ ) { number = ( number * 10 + 1 ) % K ; if ( number == 0 ) return len ; } return - 1 ; } var K = 7 ; document . write ( numLen ( K ) ) ;