Zigzag Pattern Text Conversion
Problem
Take a string and write its characters into numRows rows in a zigzag — go down to the bottom, then diagonally back up to the top, repeating. After laying out the characters, read each row left to right and concatenate. Maintain one buffer per row; when the placement row hits 0 or numRows − 1, flip the direction.
Input
s = "PAYPALISHIRING", numRows = 3Output
"PAHNAPLSIIGYIR"Row 0: P A H N. Row 1: A P L S I I G. Row 2: Y I R.
def convert(s, num_rows):
if num_rows == 1:
return s
rows = [""] * num_rows
r, d = 0, 1
for ch in s:
rows[r] += ch
if r == 0:
d = 1
elif r == num_rows - 1:
d = -1
r += d
return "".join(rows)function convert(s, numRows) {
if (numRows === 1) return s;
const rows = Array.from({ length: numRows }, () => "");
let r = 0, dir = 1;
for (const ch of s) {
rows[r] += ch;
if (r === 0) dir = 1;
else if (r === numRows - 1) dir = -1;
r += dir;
}
return rows.join("");
}class Solution {
public String convert(String s, int numRows) {
if (numRows == 1) return s;
StringBuilder[] rows = new StringBuilder[numRows];
for (int i = 0; i < numRows; i++) rows[i] = new StringBuilder();
int r = 0, dir = 1;
for (char ch : s.toCharArray()) {
rows[r].append(ch);
if (r == 0) dir = 1;
else if (r == numRows - 1) dir = -1;
r += dir;
}
StringBuilder out = new StringBuilder();
for (StringBuilder row : rows) out.append(row);
return out.toString();
}
}string convert(string s, int numRows) {
if (numRows == 1) return s;
vector<string> rows(numRows);
int r = 0, dir = 1;
for (char ch : s) {
rows[r] += ch;
if (r == 0) dir = 1;
else if (r == numRows - 1) dir = -1;
r += dir;
}
string out;
for (auto& row : rows) out += row;
return out;
}