I could not find the answer of Q4. Is it somewhere?

```
# Q1
def pleaseConfirm(caps):
caps = caps + ['END']
start = forward = backward = 0
intervals = []
for i in range(1, len(caps)):
if caps[start] != caps[i]:
intervals.append((start, i - 1, caps[start]))
if caps[start] == 'F':
forward += 1
else:
backward += 1
start = i
if forward < backward:
flip = 'F'
else:
flip = 'B'
for t in intervals:
if t[2] == flip:
if t[0] != t[1]:
print('People in positions', t[0], 'through', t[1], 'flip your caps!')
else:
print('People in positions', t[0], 'flip your caps!')
caps1 = ['F', 'F', 'B', 'B', 'B', 'F', 'B', 'B', 'B', 'F', 'F', 'B', 'F'];
caps2 = ['F', 'F', 'B', 'B', 'B', 'F', 'B', 'B', 'B', 'F', 'F', 'F', 'F'];
pleaseConfirm(caps1)
print('next')
pleaseConfirm(caps2)
```

```
# Q2
def pleaseConfirmOnePass(caps):
caps = caps + [caps[0]]
start = 0
for i in range(1, len(caps)):
if caps[i] != caps[i - 1]:
if caps[i] != caps[0]:
print('People in positions', i, end = " ")
start = i
else:
if start == i - 1:
print('flip your caps!')
else:
print('through', i - 1, 'flip your caps!')
caps1 = ['F', 'F', 'B', 'B', 'B', 'F', 'B', 'B', 'B', 'F', 'F', 'B', 'F'];
caps2 = ['F', 'F', 'B', 'B', 'B', 'F', 'B', 'B', 'B', 'F', 'F', 'F', 'F'];
pleaseConfirmOnePass(caps1)
print('next')
pleaseConfirmOnePass(caps2)
```

```
# Q3
def pleaseConfirm(caps):
caps = caps + ['END']
start = forward = backward = 0
intervals = []
for i in range(1, len(caps)):
if caps[i - 1] == 'H':
start = i
if caps[start] != caps[i]:
intervals.append((start, i - 1, caps[start]))
if caps[start] == 'F':
forward += 1
else:
backward += 1
if caps[i] != 'H':
start = i
if forward < backward:
flip = 'F'
else:
flip = 'B'
for t in intervals:
if t[2] == flip:
if t[0] != t[1]:
print('People in positions', t[0], 'through', t[1], 'flip your caps!')
else:
print('People in positions', t[0], 'flip your caps!')
caps = ['F', 'F', 'B', 'H', 'B', 'F', 'B', 'B', 'B', 'F', 'H', 'F', 'F'];
pleaseConfirm(caps)
```

```
# Q4
def encrypt(s):
s += '0'
start = 0
encrypted = ''
for i in range(1, len(s)):
if s[start] != s[i]:
encrypted += s[start] + str(i - start)
start = i
return encrypted
def decrypt(s):
character = ''
decrypted = ''
for i in range(len(s)):
if not s[i].isalpha():
decrypted += s[i - 1] * int(s[i])
return decrypted
s = 'BWWWWWBWWWW'
enc = encrypt(s)
dec = decrypt(enc)
print('encrypted=', enc, ', decrypted=', dec)
```

## Discussion (0)