6. ZigZag Conversion

ZigZag_Conversion.swift

class Solution {
    func convert(_ s: String, _ numRows: Int) -> String {
        var groups = [[String]](repeating: Array(repeating: " ", count: s.count), count: numRows)
        var idx = 0
        var v = 0
        var h = 0
        var str = ""
        var resStr = ""
        
        if numRows == 0 {
            return ""
        }
        
        if s.count <= numRows || numRows == 1 {
            return s
        }
        
        while idx < s.count {
            str = String(s[s.index(s.startIndex, offsetBy: idx)])
            groups[v][h] = str
            if v == numRows-1 {
                while v > 0 {
                    h += 1
                    v -= 1
                    idx += 1
                    str = String(s[s.index(s.startIndex, offsetBy: idx)])
                    groups[v][h] = str
                }
            }
            v += 1
            idx += 1
        }
        var tempStr = ""
        for i in 0 ..< numRows {
            for j in 0 ..< s.count {
                tempStr = groups[i][j]
                resStr += tempStr.filter({ $0 != " "})
            }
        }
        return resStr
    }
}