As previously described The Lady and the Tiger is essentially the set up for the Princess's intense conflict between her love and hate, morals and barbaric disposition. Flowers for Algernon entails the exploits of the mentally challenged Charlie Gordon, particularly his surgery to triple his intelligence. Both are focused on the mind, and the conflict thereof.
However the stories are narrated quite differently, The Lady and the Tiger from the perspective of an all knowing author, and Flowers for Algernon from the journal entries of Charlie. The stories also differ in time period, one set in a barbaric Bronze Age the other in modern day. They also have different themes, ( though both are about mind) , The Lady and the Tiger about the polar opposites of human passion, and Flowers for Algernon about the gain and subsequent loss of thought capability.
The Lady and the Tiger begins with a description of the setting and lead up to the princess's moral dilemma, and concludes with the posing of the title question to the reader. Flowers for Algernon begins with a showcase of Charlie's current grammar and spelling skills, which continue to climb throughout the course of the book. Despite the differences in layout, the decisions the readers were compelled to make were surprisingly similar. They both decided to gain knowledge, ( the princess finding out what was behind each door, and Charlie agreeing to surgery) and each had to decide what to do with the knowledge once gained.
The Telltale Heart and Flowers for Algernon exist in a possibly similar time frame, the Telltale Heart avoiding specification of time period, and Flowers for Algernon existing in a clearly modern, or possibly even futuristic world. Though not a striking similarity it sets the background for some of the similar elements, such as the character's shared desire to enact change because someone looks at them funny. (Quite a stretch I know but I'm having difficulty finding similarities) . The biggest similarity is the way in which they are both narrated each described from the main characters view with only guesses at others thoughts.
There is however a much larger pile of differences to draw on, such as the characters levels of patience, intelligence, and motives, which vary to the extreme throughout the stories. The Narrator of the Telltale Heart is quite patient at least until the moment of action comes, while Charlie is seemingly the reverse, rushing through the Rorschach and races against Algernon, until the after effects of surgery sink in. The characters begin at inverse poles of intelligence, with the Narrator at the height of strategy and planning, and Charlie refusing to pretend there are images in ink blots. As each book progresses however, thought levels change, the Narrator progressively becoming more and more insane, and Charlie beginning his enormous climb and subsequent decline of intelligence. The books also have very different themes, one relying on bloody thrills, and the consequences of murder, the other on the absoluteness of intellectual prowess.