0006.go

// Source: https://leetcode.com/problems/zigzag-conversion
// Title: ZigZag Conversion
// Difficulty: Medium
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 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
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

import (
	"strings"
)

func convert(s string, numRows int) string {
	n := len(s)
	if numRows == 1 || n <= numRows {
		return s
	}

	// Zigzag
	rows := make([]strings.Builder, numRows)
	shift := 2 * (numRows - 1)
	for i, c := range s {
		j := i % shift
		if j >= numRows {
			j = shift - j
		}
		rows[j].WriteRune(c)
	}

	// Join
	var res strings.Builder
	for _, row := range rows {
		res.WriteString(row.String())
	}

	return res.String()
}