Correct Message

Computer Science Level 1

Alice wants Chris to deliver an important message to Bob. Unfortunately, Chris is bad at memorizing and thus will make one or two characters wrong each time he sends the message. To increase the chance that Bob can derive the original message, Alice sends Chris to deliver the same message for three times. Here are the messages Bob received. Which option best describe Alice's message?

$\begin{aligned} & \text{FLYE NEW} \\ & \text{FLEE NOT} \\ & \text{FREE NOW} \end{aligned}$

\text{FREE NOW}

\text{FLEE NOW}

\text{FLYE NEW}

\text{FLEE NOT}

\text{FREE NOT}

\text{FREE NEW}

\text{FLYE NOT}

2 solutions

Jesse Nieminen
Sep 16, 2016

We compare each of the choices for the original message to the modified messages.

$\text{FLEE NOW}$ is the only one of the possible original messages which has always $1$ or $2$ wrong letters when compared to the modified messages.

Hence, the answer must be $\boxed{\text{FLEE NOW}}$

Nice and clear solution. I want to add an interesting fact.

Contrary to popular belief, data transmission is often not intact - some bits will lose here and there. Though unlikely, it is crucial in some event such as internet banking to ensure that data is not damaged in any way. Hence, error detection and correction algorithms are introduced. This problem is a variant of repetition code , a kind of error detection and correction method, where the recipient requests the original message to be sent several times to compare for a more accurate result.

Christopher Boo - 4 years, 8 months ago

Shash Manny
Sep 19, 2016

In the question we have Position 1 2 3 4 5 6 7 occupied by the letters of the phrase 1) FLYE NOW 2) FLEE NOT 3) FREE NOW When we compare 1 and 2 we see that Y and W are replaced by E and T respectively. On comparing 2 and 3 we see that L and T ate replaced by R and W respectively. Since we know that he makes only one or two mistakes we can deduce that if he had made two letters at the same position wrong in two different phrases then he would have made three errors which is not possible. Hence whichever occurs more than once in each position of the three phrases is right. since in position 2 ,L occurs twice. in position 3 ,E occurs twice and in position 7 ,W occurs twice hence we can conclude that the phrase is FLEE NOW.

ALSO IT IS THE MOST OBVIOUS CHOICE FOR A MESSAGE xD

Correct Message

2 solutions

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