6. Zigzag Conversion

Medium

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

解題

func convert(s string, numRows int) string {
	length := len(s)
	answer := ""

	if length == 0 || length<=numRows || numRows == 1 {
		return s
	}
    

	for i := 0; i < numRows; i++ {
		gap := (numRows-1)*2 - 2*i
		gap2 := (numRows-1)*2 - gap

		j := i
		answer += string(s[j])

		for {
			if gap != 0 {
				j += gap
				if j >= length {
					break
				}
				answer += string(s[j])
			}

			if gap2 != 0 {
				j += gap2
				if j >= length {
					break
				}
				answer += string(s[j])
			}
		}
	}

	return answer
}