reverse_prefix.py

# Given a 0-indexed string word and a character ch, reverse the segment of word
# that starts at index 0 and ends at the index of the first occurrence of ch (inclusive).
# If the character ch does not exist in word, do nothing.

# For example, if word = "abcdefd" and ch = "d", then you should reverse the segment that
# starts at 0 and ends at 3 (inclusive). The resulting string will be "dcbaefd".
# Return the resulting string.


# Example 1:
# Input: word = "abcdefd", ch = "d"
# Output: "dcbaefd"
# Explanation: The first occurrence of "d" is at index 3. 
# Reverse the part of word from 0 to 3 (inclusive), the resulting string is "dcbaefd".

# Example 2:
# Input: word = "xyxzxe", ch = "z"
# Output: "zxyxxe"
# Explanation: The first and only occurrence of "z" is at index 3.
# Reverse the part of word from 0 to 3 (inclusive), the resulting string is "zxyxxe".

# Example 3:
# Input: word = "abcd", ch = "z"
# Output: "abcd"
# Explanation: "z" does not exist in word.
# You should not do any reverse operation, the resulting string is "abcd".
 

# Constraints:

# 1 <= word.length <= 250
# word consists of lowercase English letters.
# ch is a lowercase English letter.


class Solution:
    def reversePrefix(self, word: str, ch: str) -> str:
        stk = []    
        i = 0    
        while i < len(word):
            stk.append(word[i])
            if word[i] == ch:
                break
            i += 1
        
        if i == len(word):
            return word
        strg = ''
        while stk:
            strg += stk.pop()
        return strg+ word[i+1:]