Initial Analysis  

  • Two (2) keys are special:

    • silly:

      • Typing silly outputs a different character (sillyOut)

        Important note:   sillyOut is not in the input stream !

    • quiet:

      • Typing silly outputs nothing

  • Additional input requirements:

    • silly appears in the input at least once
    • quiet may or may not be found in the input
    • The sequence "silly quiet" is not in input
    • The sequence "quiet silly" is not in input

  Step 1: use the first mismatched character to find quiet or silly  

  • You can find silly or quiet using the first mismatched character:

    • The first mismatched character is silly and sillyOut if: 

        input:   ---------- x x x x ... y
              same
  output:  ---------- z z z z ...

 Then:

      silly    = x
      sillyOut = z

    • The first mismatched character is quiet if: 

        input:   ---------- x x x x ... y
              same
  output:  ---------- y

 Then:

      quiet    = x

  Step 2a: silly was found in step 1, find quiet  

  • If first mismatched character was silly, then find quiet as follows:

    • If   length(input) = length(output):   quiet = -

    • Otherwise: 

        I = {input characters}  - silly
  O = {output characters} - sillyOut

  quiet = I - O

  Step 2b: quiet was found in step 1, find silly  

  • If first mismatched character was quiet, then find silly and sillyOut as follows: 

      I = {input characters}  - quiet
  O = {output characters}

  silly    = I - O 
  sillyOut = O - I

  Solution in Python   

inp  = input()     # Typed line
outp = input()     # Output line

# Find first different character in inp and outp
for i in range( len(inp) ):
   if ( inp[i] != outp[i] ):
       print(f"First diff char: {inp[i]} != {outp[i]}")

       firstDiffCharInOutp = outp[i]
       print(f"firstDiffCharInOutp = {firstDiffCharInOutp}")

       break

# Find next different char in input
for j in range(i+1, len(inp)):
   if (inp[j] != inp[i]):
      break;  

print(f"Next diff char in input = {inp[j]}")

# Find first special character (quiet or silly)
if ( firstDiffCharInOutp == inp[j] ):
   # We found "quiet"
   quiet = inp[i]
   print(f"** quiet = {quiet}")
   silly = None
   sillyOut = None
else:
   # We found "silly"
   silly = inp[i]
   print(f"** silly = {silly}")
   sillyOut = firstDiffCharInOutp
   quiet = None


# Now find the 2nd special character
inpSet  = set(inp)
outpSet = set(outp)

if ( silly == None ):
   # Find silly
   print(f"Find silly....")

   inpSet.remove(quiet)		# Remove quiet from inpSet
   diff1 = inpSet.difference(outpSet)
   silly = list(diff1)[0]

   # Find sillyOut
   diff2 = outpSet.difference(inpSet)
   sillyOut = list(diff2)[0]

else:
   # Find quiet

   if ( len(inp) == len(outp) ):
       quiet = '-'
   else:
       diff1 = inpSet.difference(outpSet)
       quiet = list(diff1)[0]

print(silly, sillyOut)
print(quiet)

  Solution in C++   

   String inp  = first line of input
   String outp = second line in input

   // Find first different character in inp and outp
   for ( int i = 0; i < length(inp); i++ )
   {
      if ( inp[i] != outp[i] )
      {
         firstDiffCharInOutp = outp[i];
         break;
      }
   }

   // Find next different char in input
   for ( j = i+1; j < length(inp); j++ )
      if ( inp[j] != inp[i] )
         break;

   // Find first special character (quiet or silly)
   if ( firstDiffCharInOutp == inp[j] )
   {  // We found "quiet"

      quiet = inp[i];
      silly = '\0';
      sillyOut = '\0';
   }
   else
   {  // We found "silly"

      silly = inp[i];
      sillyOut = firstDiffCharInOutp;
      quiet = '\0';
   }

   // Now find the 2nd special character
   inpSet  = set(inp);   // Compute the set of letter in inp
   outpSet = set(outp);  // Compute the set of letter in outp

   if ( silly == '\0' )
   {
      inpSet = inpSet - {quiet};  // Remove quiet from inpSet

      diff1 = inpSet - outpSet;
      silly = diff1[0];
   }
   else
   {
      if ( length(inp) == length(outp) )
         quiet = '-';
      else
      {
         diff1 = inpSet - outpSet;
         quiet = diff1[0];
      }
   }

   print(silly, sillyOut);
   print(quiet);