為什么只替換第一組字符？

這就是您所描述的：

encrypted = input("Enter an encrypted message: ")

count = 0
result = ''
for i, ch in enumerate(encrypted):
    if i == 0 or ch == encrypted[i-1]:
        count += 1
    else:
        result += chr(count + 64)
        count = 1
if count > 0:
    result += chr(count + 64)

print(result)

Result:

Enter an encrypted message: @##$$%%%
ABBC

它不會建立發現內容的記錄，如果需要，會將其添加回：

encrypted = input("Enter an encrypted message: ")

ch = ''
count = 0
result = ''
counts = []
for i, ch in enumerate(encrypted):
    if i == 0 or ch == encrypted[i-1]:
        count += 1
    else:
        result += chr(count + 64)
        counts.append((ch, count))
        count = 1
if count > 0:
    result += chr(count + 64)
    counts.append((ch, count))

print(result, counts)

但如果你需要它，你也可以：

encrypted = input("Enter an encrypted message: ")

ch = ''
count = 0
counts = []
for i, ch in enumerate(encrypted):
    if i == 0 or ch == encrypted[i-1]:
        count += 1
    else:
        counts.append((ch, count))
        count = 1
if count > 0:
    counts.append((ch, count))

print([chr(count+64) for _, count in counts], counts)