Camel and Banana Puzzle || Amazon Interview Puzzle

 Puzzle Details : 

The owner of a banana plantation has a camel. He wants to transport his 3000 bananas to the market, which is located after the desert. The distance between his banana plantation and the market is about 1000 kilometers. So he decided to take his camel to carry the bananas. The camel can carry at the maximum of 1000 bananas at a time, and it eats one banana for every kilometer it travels.

What is the most bananas you can bring over to your destination?

Solution:

First of all, the brute-force approach does not work. If the Camel starts by picking up the 1000 bananas and tries to reach point B, then the camel will eat up all the 1000 bananas on the way and there will be no bananas left for him to return to point A.

So we have to take an approach that the Camel drops the bananas in between and then returns to point A to pick up bananas again.

Since there are 3000 bananas and the Camel can only carry 1000 bananas, he will have to make 3 trips to carry them all to any point in between.

<---p1---><--------p2-----><-----p3---->

A---------------------------------------->B

When bananas are reduced to 2000 then the Camel can shift them to another point in 2 trips and when the number of bananas left is <= 1000, then he should not return and only move forward.

In the first part, P1, to shift the bananas by 1Km, the Camel will have to

1. Move forward with 1000 bananas – camel Will eat up 1 banana on the way forward
2. Leave 998 banana after 1 km and return with 1 banana – camel will eat up 1 banana on the way back
3. Pick up the next 1000 bananas and move forward – camel Will eat up 1 banana on the way forward
4. Leave 998 banana after 1 km and return with 1 banana – camel will eat up 1 banana on the way back
5. Will carry the last 1000 bananas from point a and move forward – camel will eat up 1 banana

After point 5 the Camel does not need to return to point A again. So to shift 3000 bananas by 1km, the Camel will eat up 5 bananas. After moving to 200 km the Camel would have eaten up 1000 bananas and is now left with 2000 bananas.

Now in Part P2, the Camel needs to do the following to shift the Bananas by 1km.

1. Move forward with 1000 bananas – camel Will eat up 1 banana on the way forward
2. Leave 998 banana after 1 km and return with 1 banana – camel will eat up this 1 banana on the way back
3. Pick up the next 1000 bananas and move forward – camel Will eat up 1 banana on the way forward

After point 3 the Camel does not need to return to the starting point of P2. So to shift 2000 bananas by 1km, the Camel will eat up 3 bananas. After moving to 333 km the camel would have eaten up 1000 bananas and is now left with the last 1000 bananas.

The Camel will actually be able to cover 333.33 km, I have ignored the decimal part because it will not make a difference in this example.

Hence the length of part P2 is 333 Km.

Now, for the last part, P3, the Camel only has to move forward. He has already covered 533 (200+333) out of 1000 km in Parts P1 & P2. Now he has to cover only 467 km and he has 1000 bananas.

The camel will eat up 467 bananas on the way forward, and at point B the Camel will be left with only 533 Bananas.