if character from both string is not same then we take the minimum from three specified operation
else { DP [ i % 2 ] [ j ] = 1 + min ( DP [ ( i - 1 ) % 2 ] [ j ] , min ( DP [ i % 2 ] [ j - 1 ] , DP [ ( i - 1 ) % 2 ] [ j - 1 ] ) ) ; } } }