package cap3

// Ex21 螺旋阵
func Ex21(n int) [][]int {
    matrix := _makeMatrix(n)

    // 逐层往里填充
    num := 1
    for layer := 0; layer < n/2; layer++ {
        // 方阵左边
        for i := layer; i < n-layer; i++ {
            matrix[i][layer] = num
            num++
        }

        // 方阵下边
        for i := layer + 1; i < n-layer; i++ {
            matrix[n-layer-1][i] = num
            num++
        }

        // 方阵右边
        for i := n - layer - 2; i >= layer; i-- {
            matrix[i][n-layer-1] = num
            num++
        }

        // 方阵上边
        for i := n - layer - 2; i > layer; i-- {
            matrix[layer][i] = num
            num++
        }
    }

    // 奇数阶中间位置需要手动设置
    if n%2 != 0 {
        matrix[n/2][n/2] = n * n
    }

    return matrix
}

func Ex21type2(n int) [][]int {
    matrix := _makeMatrix(n + 10)

    row, col, t := 0, 0, 1

    for i := 0; i < n*n; {
        for j := 0; j < 2*n; j++ {
            i++
            matrix[row][col] = i

            switch (j + 1) / (n + 1) {
            case 0:
                row += t
            case 1:
                col += t
            }
        }

        n--
        t = -t
    }

    return matrix
}