balls-1000

balls-1000

Description

There are 12 balls, all of equal size, but only 11 are of equal weight, one fake ball is either lighter or heavier. Can you find the fake ball by using a balance scale only 3 times?

nc 34.68.81.63 6666

Solution

If we connect to the server we get something like

We just need to find the ligther or heavier ball.

You can read about this problem on wikipedia/Balance_puzzle

@comet was able to create a script to solve this

#https://wordplay.blogs.nytimes.com/2014/07/21/12coin/
from pwn import *
r = remote('34.68.81.63', 6666)
for i in range(9):
    r.recvline()
while True:
    print(r.recvline()) # ROUND
    ans = 0
    r.sendlineafter(': ','1,2,3,4 5,6,7,8')
    print('1,2,3,4 5,6,7,8')
    s = r.recvline()
    print(s)
    if 'equally' in s:
        r.sendlineafter(': ','9,10,11 1,2,3')
        print('9,10,11 1,2,3')
        s = r.recvline()
        print(s)
        if 'equally' in s:
            ans = 12
            r.sendlineafter(': ','1 2')
        elif 'left is lighter' in s:
            r.sendlineafter(': ','9 10')
            print('9 10')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 11
            elif 'left is lighter' in s:
                ans = 9
            else:
                ans = 10
        else:
            r.sendlineafter(': ','9 10')
            print('9 10')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 11
            elif 'left is lighter' in s:
                ans = 10
            else:
                ans = 9
    elif 'left is lighter' in s:
        r.sendlineafter(': ','1,2,5 3,4,6')
        print('1,2,5 3,4,6')
        s = r.recvline()
        print(s)
        if 'equally' in s:
            r.sendlineafter(': ','7 8')
            print('7 8')
            s = r.recvline()
            print(s)
            if 'left is lighter' in s:
                ans = 8
            else:
                ans = 7
        elif 'left is lighter' in s:
            r.sendlineafter(': ','1 2')
            print('1 2')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 6
            elif 'left is lighter' in s:
                ans = 1
            else:
                ans = 2
        else:
            r.sendlineafter(': ','3 4')
            print('3 4')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 5
            elif 'left is lighter' in s:
                ans = 3
            else:
                ans = 4
    else:
        r.sendlineafter(': ','1,2,5 3,4,6')
        print('1,2,5 3,4,6')
        s = r.recvline()
        print(s)
        if 'equally' in s:
            r.sendlineafter(': ','7 8')
            print('7 8')
            s = r.recvline()
            print(s)
            if 'left is lighter' in s:
                ans = 7
            else:
                ans = 8
        elif 'left is lighter' in s:
            r.sendlineafter(': ','3 4')
            print('3 4')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 5
            elif 'left is lighter' in s:
                ans = 4
            else:
                ans = 3
        else:
            r.sendlineafter(': ','1 2')
            print('1 2')
            s = r.recvline()
            print(s)
            if 'equally' in s:
                ans = 6
            elif 'left is lighter' in s:
                ans = 2
            else:
                ans = 1
    print(ans)
    r.sendlineafter(':\n',str(ans))
    print(r.recvline())

You can run this script in the DEBUG mode, it will run for 50 ROUNDS

FLAG: ISITDTU{y0u_hav3_200iq!!!!}

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Something funnier that happend while people were joining the channel for this challenge.