867. Transpose Matrix

矩阵转换，注意下标索引的正确映射。

class Solution {
    func transpose(_ A: [[Int]]) -> [[Int]] {
        guard A.count >= 1 && A[0].count >= 1 else {
            return [[Int]]()
        }
        
        var a: [Int] = Array(repeating: 0, count: A.count)
        var ret: [[Int]] = Array(repeating: a, count: A[0].count)
        
        for j in 0..<A[0].count {
            for i in 0..<A.count {
                ret[j][i] = A[i][j]
            }
        }
        
        return ret
    }
}