# Questions tagged [river-crossing]

For questions regarding how to get items or people across something obeying a set of rules.

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### Nothing but pairs of a kind

The objective is to reduce a given word to nothing in a series of steps. At each step, remove every occurrence of an adjacent pair of letters of your choosing. For example: Problem: Reduce ...
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### River crossing cats and dogs

A farmer and his $n$ cats and $m$ dogs are on one side of a river. There is a boat that can carry the farmer and at most $k$ animals at once. The boat doesn't move without a person operating it. The ...
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189 views

### Crossing desert with smallest amount of water [duplicate]

A man who lives in a desert sends his servant out to collect the flag which is 4 miles away from the man's home. To survive the servant must drink 1 litre of water on every mile he walks (so the ...
213 views

### Wounded Soldiers/Crossing a Bridge Puzzle - checking a solution

I am working on a Prolog university assignment, where we have to determine what the shortest time is for 4 wounded soldiers to cross a bridge to safety. This seems to be a variation of the more common ...
214 views

### Triple up, pair off, and single out

Can you transform this word triple PELTS SORES DIVAN into this word triple PLOTS DIVES SANER just by swapping pairs of ...
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### An overcomplicated Boat Puzzle

Based on Xkcd's Boat Puzzle At the riverbank, a succession of people have given you a large lump of objects to transport across the river. These are: 101 cabbages 2 goats, one of which eats wolves 4 ...
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208 views

### A small pond-crossing

While walking through the flower gardens, you encounter a small group of fairies stuck on a lilypad. There are 2 red fairies, 2 yellow fairies, and 2 green fairies, and they have nothing besides a ...
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195 views

### A frugal canal-crossing

You've been sent out to round up some escaped animals. While you have some of them under control now, you've ended up trapped on the wrong side of a canal. Currently, you have 5 animals: A perivine, ...
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3k views

### Escape across the floorboards

A mad lexophile sits alone in his apartment obsessively rearranging his Scrabble tiles and writing words on every available surface, even filling each floorboard with a word. The Scrabble tiles have ...
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172 views

### Crossing a river with bonds and beefs

Here is a river crossing puzzle (note that whenever I use the term "colors", I mean the squares): Yellow and Red are on one side of the river, while Pink, Blue, Green and Black are on the ...
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### A river crossing puzzle

Here is a puzzle I came up with. Ali and Billie are approaching a river from one side, and Casey and Devin from the other side. Ali shouts: "Do you two also want to cross?" Casey shouts back:...
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### Minimum time to cross the bridge

There are 6 friends A, B, C, D, E and F who want to cross a bridge. However, there are two problems. First, the bridge can only accommodate two persons at a time. Second, it is night and they need the ...
301 views

### Strait-Crossing Puzzle

You are on an island, and must transport 3 moose across a strait to the mainland. While they can swim across the strait, they will likely end up running into the forest and leaving you behind. While ...
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207 views

### How do I find the least number of times a shuttle can travel from one place to another?

I often see this situation in exams and I'd like to know if there is any kind of algorithm or shortcut that I can use to solve this puzzle instead of just guessing. The problem is as follows: A space ...
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200 views

### Terrorists transporting Hostages through the desert

You belong to an intelligence agency that is monitoring some terrorists. There are three of them in the Hideout A with three hostages and a bomb. Unfortunately, this hideout is extremely secure. But ...
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337 views

### Family river-crossing

A family of six is crossing a river with a 2-passenger boat. The family includes the following members: Dad, Mom, Maid, Boy, Girl & Dog. Only the 3 adults can row the boat and the dog counts as a ...
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313 views

### Missing lattes and mutually mistrustful words

It's always amusing to watch two kids who don't trust each other swap baseball cards by exchanging them at exactly the same moment. Words can be equally mistrustful about trading their letters. ...
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### Boat children and army crossing the river puzzle

During the war, a small detachment found itself confronted by a deep and wide river. However, they found a small boat in which two-children were rowing about. It was a very small boat and can only ...
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383 views

### Don't look back, crazy clown

Start with these two words INSANE RETROSPECT and see if you can get them to exchange places by transferring one letter at a time. With each ...
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### Uncover Lenny Fingers' street hustle

Lenny Fingers is out on the street again, hustling people with his shell games. This time, he's using words. As you walk by, Lenny grabs you with an enthusiastic smile and shows you two words side-...
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### The cat exchanges places with a drawing of the cat

Given CAT RENDERING see if you can get them to exchange places, resulting in RENDERING CAT by ...
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### Farmer needs to get his word across the river

In the spirit of the classic river-crossing puzzles: ...
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570 views

### Rigorous way to solve the river crossing problem

I encountered this classic brain teaser: Four people, A, B, C and D need to get across a river. The only way to cross the river is by an old bridge, which holds at most 2 people at a time. ...
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### Another river with some extra letters

2 men are at a river. There is a boat. It holds only one person at a time. They both cross the river and continue their way... How? P.S. No Uber, helicopters, bridges, ropes, or anything else close ...
1k views

### numbers want to cross a river, but their sum must be a square number

In the world of numbers, numbers 1 to 9 want to cross a river, They have a boat which can take 1 to 3 numbers, But sum of the numbers must be a square number. The boat can not sail back itself, so ...
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### Ali Baba and the 10 thieves

EDIT: This puzzle originates from the "International Mathematics Tournament of the Towns", and was published in the book "S.M.A.R.T circle overview" by Professor Andy Liu. The author has (albeit a ...
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1 vote
2k views

### 3 cannibals and 3 missionaries on different side of the river

Three missionaries on the left side of a river and three cannibals on the right side of the river want to cross a river using a boat which can carry at most two people, The boat is on the cannibals ...
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### When do missionaries and cannibals problems have solutions?

In the Missionaries and Cannibals problem: Three missionaries and three cannibals must cross a river using a boat which can carry at most two people, under the constraint that, for both banks, ...
2k views

### Zombie horde incoming! [duplicate]

Here is a puzzle I found on youtube's Ted-ed channel and found quite fun to solve. You and 3 more people are for some reason running away from a horde of zombies in the darkness while holding a ...
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967 views

### Cross the river with a small (4 spaces) boat

Giant, Slimy, Boy, Romy and Fatty want to cross a river. To cross the river there is a small boat. The boat only has 4 spaces. Every one can row the boat. At the boat, Giant needs 4 spaces. Slimy ...
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### River Crossing Puzzle

There is a family which contains 4 members: Dad, Mom, Son, Daughter. They have a boat which carries only 100 kg at a time. Mom and Dad weigh 100 kg each, while Son and Daughter weigh 50 kg each. ...
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### Quick!!! You got only 30 seconds

There are two checkpoints on a road namely Pt. A and Pt. B. There are 5 persons standing at the Pt. A namely P , Q , R , S, T. They have a car such that P , Q , R , S , T can travel to Pt. B in 1 , 3 ,...
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200 views

### Ancient mysteries of the Arab world [duplicate]

If we want to convey the lion and the sheep and feed from the bank of the river to the other how to do it? and the lion will not eat the sheep and the sheep will not eat the feed
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### Bridge's riddle [duplicate]

You're in a group of people going for an internship in a remote mountain lab. By mistake you pulled a lever with a skull just out of curiosity and it released some zombies. So you and your group had ...
1 vote
1k views

### Crossing The River (Humans And Monsters Puzzle With A Twist)

3 couples on one side of a river. Aa Bb Cc (caps representing husbands, lowercase representing wives) One boat in which 2 people can travel at a time. At least one person must row the boat wherever ...
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### Numbers nonexistent

This problem is one of the hardest problems I have ever encountered. If you don't trust links, here it is: There are some Couples wanting to cross a river by a boat. The boat can carry at most 3 ...
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### A man, a chicken, and a fox? [duplicate]

A man lives in a small house with a farm as his back garden and has a river beside his house. On the other side of the river is a shop. One day, he visited the shop, he bought a chicken and a fox for ...
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### Can you solve this Bruce Wayne logic puzzle?

This variation of the classical Farmer Goat puzzle was in a puzzle contest at my college two years ago. Here it goes. Mr. Bruce Wayne is very fond of parties. Well, he’s more fond of girls, but, ...
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### How can the animals get across the river without a fight breaking out?

There are three dogs and three cats that have to be transported across a river: a big dog, a medium dog and a small dog, a big cat, a medium cat, and a small cat. Rules: The raft can carry two ...
• 369
6k views

### The case of the 4 campers and the rickety bridge! [duplicate]

Four people need to cross a rickety rope bridge to get back to their camp at night. Unfortunately, they only have one flashlight and it only has enough battery left for seventeen minutes. The bridge ...
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3k views

### $n$ couples crossing a river

There are $n$ couples on one side of the river. Nobody is on the other side. They have a boat that accommodates up to 2 people. For every trip across, someone(s) must bring the boat back as well. The ...
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475 views

### $n$ monsters and $n$ people

There are $n$ monsters (M) and $n$ people (P) on the left side of a river. Nobody is on the right. They have a boat that can hold up to 2 beings. At no point on time may either of these be true: M_{...
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### How can the man get across the river with the two animals and the cabbage? [duplicate]

A man has a wolf, a goat, and a cabbage. He must cross a river with the two animals and the cabbage. There is a small rowing boat, in which he can take only one thing with him at a time. If, however, ...
884 views

### A Fox, a Chicken, a Pile of Seeds, and a Boat [duplicate]

There's 2 islands, 1 island has a pile of seeds, a chicken, and a fox. There's also a boat next to this island, you have to get it all across with minimum uses of the boat. You can only take one ...
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### Fastest way to cross a river: four people with different rowing speeds

This problem is commonly cited as a Microsoft interview problem, although I have paraphrased it here to involve a river and a boat instead of a bridge and a flashlight, and tweaked the crossing times ...
47k views

### Strategy to solve the Missionaries and Cannibals problem

In the Missionaries and Cannibals problem: Three missionaries and three cannibals must cross a river using a boat which can carry at most two people, under the constraint that, for both banks and ...
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