起因
同学的朋友读计算机语言，然后有道题目。
具体题目要求：
需要用到的预设函数：
# bmrs
def bmrs(word, i=1):
if not word.startswith('_'):
word = '_' + word
if -1 < i < len(word):
return interpret(word, i) + bmrs(word, i+1)
return ''
# predecessor
def p(word, i):
if i <= 1:
return 0
else:
return i-1
# successor
def s(word, i):
if i >= len(word) - 1:
return 0
else:
return i+1
# interpreter function
def interpret(word, i):
if H_o(word, i):
return 'H'
else:
if L_o(word, i):
return 'L'
else:
return '0'
# input predicate for high tones
def H_i(word, i):
return word[i] == 'H'
# input predicate for low tones
def L_i(word, i):
return word[i] == 'L'
# input predicate for out of bounds symbol
def out_of_bounds_i(word, i):
return word[i] == "_"思路和想法
肯定是要通过def H_o和L_o还有interpreter进行输出移位。
题目意思就是给进来一个由'H'、'L'、'0' 组成的字符串，左边的 'H' 尽量向右移到倒数第二或者到 'L' 的左边；如果最后一位是 'H' ，'H' 就向左移一位，如果最后一位是 'H' ，倒数第二位是'L' 就把 'H' 变成 '0'。
我自己的思路就是：构造一个新的函数，先遍历找出'H'和'L'的位置，通过enum或者index再对'H'进行移位或者替换。在可能存在多个 'L' 的情况下，'H' 将尽可能向右移动到倒数第二或者到它向右接触的第一个 'L' 的左边。如果最后一位是 'H'，则 'H' 向左移一位；如果最后一位是 'H' 且倒数第二位是 'L'，则将 'H' 变成 '0'。
接着就是对代码编写
# Function to swap characters in a word
def Swap_Char(word):
# Convert the input to a string in case it's not
word = str(word)
# Create a list of characters from the word
word_list = list(word)
# Initialize position for 'H' as None and list to keep track of 'L' positions
h_pos = None
l_positions = []
# Find the positions of 'H' and all 'L's
for i, char in enumerate(word_list):
if char == 'H':
h_pos = i
elif char == 'L':
l_positions.append(i)
# Check if 'H' exists
if h_pos is not None:
# If 'H' is at the end and the second to last is 'L', change 'H' to '0'
if h_pos == len(word_list) - 1:
if len(word_list) > 1 and word_list[-2] == 'L':
word_list[-1] = '0'
else:
# Move 'H' one position to the left
word_list[-1], word_list[-2] = word_list[-2], word_list[-1]
else:
# If 'H' is not at the end, find the first 'L' to the right of 'H'
next_l_pos = next((pos for pos in l_positions if pos > h_pos), None)
# If there is an 'L' to the right of 'H'
if next_l_pos:
# Move 'H' to the left of this 'L'
target_pos = next_l_pos - 1
else:
# Move 'H' to the second last position if it's not already there and not at the end
target_pos = len(word_list) - 2
# Swap 'H' with the target position if it's to the right
if target_pos > h_pos:
word_list[h_pos], word_list[target_pos] = word_list[target_pos], word_list[h_pos]
return ''.join(word_list)
# Output predicate for high tones
def H_o(word,i):
# Swap characters in the word first
new_word = Swap_Char(word)
# Check if the character at index i is 'H'
if len(new_word) > i and new_word[i] == 'H':
return True
else:
return False
# Output predicate for low tones
def L_o(word,i):
new_word = Swap_Char(word)
if len(new_word) > i and new_word[i] == 'L':
return True
else:
return False
# bmrs
def bmrs(word, i=1):
if not word.startswith('_'):
word = '_' + word
if -1 < i < len(word):
return interpret(word, i) + bmrs(word, i+1)
return ''
# predecessor
def p(word, i):
if i <= 1:
return 0
else:
return i-1
# successor
def s(word, i):
if i >= len(word) - 1:
return 0
else:
return i+1
# interpreter function
def interpret(word, i):
if H_o(word, i):
return 'H'
else:
if L_o(word, i):
return 'L'
else:
return '0'
# input predicate for high tones
def H_i(word, i):
return word[i] == 'H'
# input predicate for low tones
def L_i(word, i):
return word[i] == 'L'
# input predicate for out of bounds symbol
def out_of_bounds_i(word, i):
return word[i] == "_"
# Example usage
input_string = "_H000L000" #the output should be "000HL000"
print(bmrs(input_string))
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