Golang program to print a matrix in Spiral Format

Draw 2D matrix, print all elements of the given matrix in Spiral format. Given a number n, print a n x n spiral matrix (of numbers from 1 to n x n) in clockwise direction using O(1) space.
// Draw Spiral in Golang
package main
  
import (
    "fmt"
)
  
func spiral(n int) []int {
    left, top, right, bottom := 0, 0, n-1, n-1
    sz := n * n
    s := make([]int, sz)
    i := 0
    for left < right {
        // work right, along top
        for c := left; c <= right; c++ {
            s[top*n+c] = i
            i++
        }
        top++
        // work down right side
        for r := top; r <= bottom; r++ {
            s[r*n+right] = i
            i++
        }
        right--
        if top == bottom {
            break
        }
        // work left, along bottom
        for c := right; c >= left; c-- {
            s[bottom*n+c] = i
            i++
        }
        bottom--
        // work up left side
        for r := bottom; r >= top; r-- {
            s[r*n+left] = i
            i++
        }
        left++
    }
    // center (last) element
    s[top*n+left] = i
  
    return s
}
  
func main() {
    num := 5
    len := 2
    for i, draw := range spiral(num) {
        fmt.Printf("%*d ", len, draw)
        if i%num == num-1 {
            fmt.Println("")
        }
    }
}
Spiral Matrix

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