func rotate(matrix [][]int) {
if matrix == nil || len(matrix) == 0 || len(matrix) == 1 {
return
}
n := len(matrix)
tmp := make([][]int, n)
for idx := range tmp {
tmp[idx] = make([]int, n)
}
for i, item := range matrix {
for j, cell := range item {
tmp[j][n-i-1] = cell
}
}
copy(matrix, tmp)
}