006.go

package p006

/**
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 text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".
*/

import (
	"bytes"
)

func convert(s string, numRows int) string {
	if numRows <= 1 {
		return s
	}
	sLen := len(s)
	var result bytes.Buffer
	zzStep := (numRows - 1) * 2
	for i := 0; i < numRows; i++ {
		for base := i; base < sLen; base += zzStep {
			result.WriteByte(s[base])
			if i > 0 && i < numRows-1 {
				ti := base + (numRows-1-i)*2
				if ti < sLen {
					result.WriteByte(s[ti])
				}
			}
		}
	}
	return result.String()
}