# Missionaries and Cannibals

Last Updated : 18 Jan, 2023

Question: 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, if there are missionaries present on the bank, they cannot be outnumbered by cannibals (if they were, the cannibals would eat the missionaries). The boat cannot cross the river by itself with no people on board.

Solution: First let us consider that both the missionaries (M) and cannibals(C) are on the same side of the river. Left Right Initially the positions are : 0M , 0C and 3M , 3C (B) Now letâ€™s send 2 Cannibals to left of bank : 0M , 2C (B) and 3M , 1C Send one cannibal from left to right : 0M , 1C and 3M , 2C (B) Now send the 2 remaining Cannibals to left : 0M , 3C (B) and 3M , 0C Send 1 cannibal to the right : 0M , 2C and 3M , 1C (B) Now send 2 missionaries to the left : 2M , 2C (B) and 1M . 1C Send 1 missionary and 1 cannibal to right : 1M , 1C and 2M , 2C (B) Send 2 missionaries to left : 3M , 1C (B) and 0M , 2C Send 1 cannibal to right : 3M , 0C and 0M , 3C (B) Send 2 cannibals to left : 3M , 2C (B) and 0M , 1C Send 1 cannibal to right : 3M , 1C and 0M , 2C (B)’ Send 2 cannibals to left : 3M , 3C (B) and 0M , 0C â€¢ Here (B) shows the position of the boat after the action is performed. Therefore all the missionaries and cannibals have crossed the river safely.

This is the game where you must try to solve the problem with minimum number of attempts :

## Python3

 `#Python program to illustrate Missionaries & cannibals Problem  ` `#This code is contributed by Sunit Mal ` `print``(``"\n"``) ` `print``(``"\tGame Start\nNow the task is to move all of them to right side of the river"``) ` `print``(``"rules:\n1. The boat can carry at most two people\n2. If cannibals num greater than missionaries then the cannibals would eat the missionaries\n3. The boat cannot cross the river by itself with no people on board"``) ` `lM ``=` `3`            `#lM = Left side Missionaries number  ` `lC ``=` `3`            `#lC = Laft side Cannibals number  ` `rM``=``0`            `#rM = Right side Missionaries number  ` `rC``=``0`            `#rC = Right side cannibals number  ` `userM ``=` `0`        `#userM = User input for number of missionaries for right to left side travel ` `userC ``=` `0`        `#userC = User input for number of cannibals for right to left travel   ` `k ``=` `0` `print``(``"\nM M M C C C |     --- | \n"``) ` `try``: ` `    ``while``(``True``): ` `        ``while``(``True``): ` `            ``print``(``"Left side -> right side river travel"``) ` `            ``#uM = user input for number of missionaries for left to right travel  ` `            ``#uC = user input for  number of cannibals for left to right travel  ` `            ``uM ``=` `int``(``input``(``"Enter number of Missionaries travel => "``))     ` `            ``uC ``=` `int``(``input``(``"Enter number of Cannibals travel => "``)) ` ` `  `            ``if``((uM``=``=``0``)``and``(uC``=``=``0``)): ` `                ``print``(``"Empty travel not possible"``) ` `                ``print``(``"Re-enter : "``) ` `            ``elif``(((uM``+``uC) <``=` `2``)``and``((lM``-``uM)>``=``0``)``and``((lC``-``uC)>``=``0``)): ` `                ``break` `            ``else``: ` `                ``print``(``"Wrong input re-enter : "``) ` `        ``lM ``=` `(lM``-``uM) ` `        ``lC ``=` `(lC``-``uC) ` `        ``rM ``+``=` `uM ` `        ``rC ``+``=` `uC ` ` `  `        ``print``(``"\n"``) ` `        ``for` `i ``in` `range``(``0``,lM): ` `            ``print``(``"M "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,lC): ` `            ``print``(``"C "``,end``=``"") ` `        ``print``(``"| --> | "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,rM): ` `            ``print``(``"M "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,rC): ` `            ``print``(``"C "``,end``=``"") ` `        ``print``(``"\n"``) ` ` `  `        ``k ``+``=``1` ` `  `        ``if``(((lC``=``=``3``)``and` `(lM ``=``=` `1``))``or``((lC``=``=``3``)``and``(lM``=``=``2``))``or``((lC``=``=``2``)``and``(lM``=``=``1``))``or``((rC``=``=``3``)``and` `(rM ``=``=` `1``))``or``((rC``=``=``3``)``and``(rM``=``=``2``))``or``((rC``=``=``2``)``and``(rM``=``=``1``))): ` `            ``print``(``"Cannibals eat missionaries:\nYou lost the game"``) ` ` `  `            ``break` ` `  `        ``if``((rM``+``rC) ``=``=` `6``): ` `            ``print``(``"You won the game : \n\tCongrats"``) ` `            ``print``(``"Total attempt"``) ` `            ``print``(k) ` `            ``break` `        ``while``(``True``): ` `            ``print``(``"Right side -> Left side river travel"``) ` `            ``userM ``=` `int``(``input``(``"Enter number of Missionaries travel => "``)) ` `            ``userC ``=` `int``(``input``(``"Enter number of Cannibals travel => "``)) ` `             `  `            ``if``((userM``=``=``0``)``and``(userC``=``=``0``)): ` `                    ``print``(``"Empty travel not possible"``) ` `                    ``print``(``"Re-enter : "``) ` `            ``elif``(((userM``+``userC) <``=` `2``)``and``((rM``-``userM)>``=``0``)``and``((rC``-``userC)>``=``0``)): ` `                ``break` `            ``else``: ` `                ``print``(``"Wrong input re-enter : "``) ` `        ``lM ``+``=` `userM  ` `        ``lC ``+``=` `userC ` `        ``rM ``-``=` `userM ` `        ``rC ``-``=` `userC ` ` `  `        ``k ``+``=``1` `        ``print``(``"\n"``) ` `        ``for` `i ``in` `range``(``0``,lM): ` `            ``print``(``"M "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,lC): ` `            ``print``(``"C "``,end``=``"") ` `        ``print``(``"| <-- | "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,rM): ` `            ``print``(``"M "``,end``=``"") ` `        ``for` `i ``in` `range``(``0``,rC): ` `            ``print``(``"C "``,end``=``"") ` `        ``print``(``"\n"``) ` ` `  `     `  ` `  `        ``if``(((lC``=``=``3``)``and` `(lM ``=``=` `1``))``or``((lC``=``=``3``)``and``(lM``=``=``2``))``or``((lC``=``=``2``)``and``(lM``=``=``1``))``or``((rC``=``=``3``)``and` `(rM ``=``=` `1``))``or``((rC``=``=``3``)``and``(rM``=``=``2``))``or``((rC``=``=``2``)``and``(rM``=``=``1``))): ` `            ``print``(``"Cannibals eat missionaries:\nYou lost the game"``) ` `            ``break` `except` `EOFError as e: ` `    ``print``(``"\nInvalid input please retry !!"``)`

Output

```    Game Start
Now the task is to move all of them to right side of the river
rules:
1. The boat can carry at most two people
2. If cannibals num greater than missionaries then the cannibals would eat the missionaries
3. The boat cannot cross the river by itself with no people on board

M M M C C C |     --- |

Left side -> right side river travel
Enter number of Missionaries travel =>