python N 字形变换 多种解法

解法一：使用二维数组

def convert(s, numRows):
    if numRows == 1 or numRows >= len(s):
        return s
    
    rows = [''] * numRows
    index, step = 0, 1
    
    for char in s:
        rows[index] += char
        
        if index == 0:
            step = 1
        elif index == numRows - 1:
            step = -1
            
        index += step
    
    return ''.join(rows)

解法二：使用列表存储每行的字符

def convert(s, numRows):
    if numRows == 1 or numRows >= len(s):
        return s
    
    rows = [[] for _ in range(numRows)]
    index, step = 0, 1
    
    for char in s:
        rows[index].append(char)
        
        if index == 0:
            step = 1
        elif index == numRows - 1:
            step = -1
            
        index += step
    
    result = ''
    for row in rows:
        result += ''.join(row)
    
    return result

解法三：直接计算字符在每行的索引位置

def convert(s, numRows):
    if numRows == 1 or numRows >= len(s):
        return s
    
    n = len(s)
    cycle_len = 2 * numRows - 2
    result = ''
    
    for i in range(numRows):
        for j in range(i, n, cycle_len):
            result += s[j]
            
            if i != 0 and i != numRows - 1 and j + cycle_len - 2 * i < n:
                result += s[j + cycle_len - 2 * i]
    
    return result