[LeetCode] ZigZag Conversion

題目鏈接：https://leetcode.com/problems/zigzag-conversion/submissions/

思路：

假設最後一個頂點總是在上面的，會有如下兩種情況：

func convert(s string, numRows int) string {
    if 1 == numRows {
		return s
	}
	bytes := []byte(s)
	maxIndex := len(s) - 1
	knots := maxIndex/(numRows-1) + 1
	upKnots := knots/2 + 1
	ret := []byte{}
	distance := 0
	for i := 0; i < numRows-1; i++ {
		for j := 0; j < upKnots; j++ {
			upIdx := j * 2 * (numRows - 1)
			if 0 == distance {
				//the up knot
				if upIdx <= maxIndex {
					ret = append(ret, bytes[upIdx])
				}
				continue
			}
			foreIdx := upIdx - distance
			latterIdx := upIdx + distance
			if foreIdx >= 0 && foreIdx <= maxIndex {
				ret = append(ret, bytes[foreIdx])
			}
			if latterIdx <= maxIndex {
				ret = append(ret, bytes[latterIdx])
			}
		}
		distance++
	}
	//the last row
	for j := 0; j < knots/2; j++ {
		ret = append(ret, bytes[(2*j+1)*(numRows-1)])
	}

	return string(ret)
}