28: number spiral diagonals

28_number_spiral_diagonals/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+func main() {
+	nums, _ := findSprialDiagonals(1001)
+	sum := 0
+	for _, n := range nums {
+		sum += n
+	}
+	fmt.Printf("nums=%v\nsum=%d\n", nums, sum)
+}
+
+func findSprialDiagonals(width int) ([]int, error) {
+	if width%2 == 0 {
+		return nil, errors.New("invalid width")
+	}
+	x := 3
+	ret := []int{1}
+	cw := 3
+	d := 2
+	for width/cw > 0 {
+		ret = append(ret, []int{x, x + d, x + 2*d, x + 3*d}...)
+		x = x + 3*d + cw + 1
+		cw += 2
+		d = cw - 1
+	}
+	return ret, nil
+}