Data commit

Task/Doomsday-rule/Go/doomsday-rule.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+    "fmt"
+    "strconv"
+)
+
+var days = []string{"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"}
+
+func anchorDay(y int) int {
+    return (2 + 5*(y%4) + 4*(y%100) + 6*(y%400)) % 7
+}
+
+func isLeapYear(y int) bool { return y%4 == 0 && (y%100 != 0 || y%400 == 0) }
+
+var firstDaysCommon = []int{3, 7, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5}
+var firstDaysLeap = []int{4, 1, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5}
+
+func main() {
+    dates := []string{
+        "1800-01-06",
+        "1875-03-29",
+        "1915-12-07",
+        "1970-12-23",
+        "2043-05-14",
+        "2077-02-12",
+        "2101-04-02",
+    }
+
+    fmt.Println("Days of week given by Doomsday rule:")
+    for _, date := range dates {
+        y, _ := strconv.Atoi(date[0:4])
+        m, _ := strconv.Atoi(date[5:7])
+        m--
+        d, _ := strconv.Atoi(date[8:10])
+        a := anchorDay(y)
+        f := firstDaysCommon[m]
+        if isLeapYear(y) {
+            f = firstDaysLeap[m]
+        }
+        w := d - f
+        if w < 0 {
+            w = 7 + w
+        }
+        dow := (a + w) % 7
+        fmt.Printf("%s -> %s\n", date, days[dow])
+    }
+}