Day021 - 6. Zigzag Conversion

6. Zigzag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P     I    N
A   L S  I G
Y A   H R
P     I

Example 3:

Input: s = "A", numRows = 1
Output: "A"

Constraints:

• 1 <= s.length <= 1000
• s consists of English letters (lower-case and upper-case), ',' and '.'.
• 1 <= numRows <= 1000

내 풀이

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        # 1줄일 때 예외처리
        if numRows == 1:
            return s
        
        main_start = 0
        sub_start = numRows
        sub_counter = 1
        row_check = 1
        answer = ""

        while row_check <= numRows:
            if row_check == 1 or row_check == numRows:
                while main_start < len(s):
                    answer += s[main_start]
                    main_start += numRows + (numRows-2)
                main_start = 1
                row_check += 1
                print(answer)
            else:
                while main_start < len(s):
                    answer += s[main_start]
                    main_start += numRows + (numRows-2)
                    try: # 대각선 부분 끊어질 때 예외처리
                        answer += s[sub_start + (numRows-2) - sub_counter]
                        sub_start += numRows + (numRows-2)
                    except:
                        pass
                
                sub_start = numRows
                sub_counter += 1
                row_check += 1
                main_start = row_check - 1
     
        return answer

이번 문제는 머리를 좀 써서 풀어야 하는 어려운 문제였다.

# Time Complexity : \(O(N)\)

 3 row면 1글자가 중간에 걸침
    4 row면 2글자가 중간에 걸침

    3 row
    "[PAY]P[ALI]S[HIR]I[NG]"
    
    4 row
    "[PAYP]AL[ISHI]RI[NG]"

    n개씩 slicing하고 n-2개만큼 건너뛰면 세로줄.
    첫줄은 세로줄만
    두 번째 줄은 세로줄 1글자(-1번째)
    세 번째 줄은 세로줄 1글자(-2번째)
    네 번째(마지막) 세로줄