LeetCode 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

Solution:

English Version in Youtube

中文版解答Youtube Link

中文版解答Bilibili Link

class Solution {
public:
    string convert(string s, int numRows) {
        if (numRows == 1) {
            return s;
        }
        
        vector<string> rows(numRows);
        int row = 0;
        int step = 1;
        for (char ch : s) {
            rows[row].push_back(ch);
            
            if (row == (numRows - 1)) {
                step = -1;
            } else if (row == 0) {
                step = 1;
            }
            row += step;
        }
        
        stringstream ss;
        for (const string& row : rows) {
            ss << row;
        }
        return ss.str();
    }
};