Data commit

Task/Canonicalize-CIDR/Go/canonicalize-cidr.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+    "fmt"
+    "log"
+    "strconv"
+    "strings"
+)
+
+func check(err error) {
+    if err != nil {
+        log.Fatal(err)
+    }
+}
+
+// canonicalize a CIDR block: make sure none of the host bits are set
+func canonicalize(cidr string) string {
+    // dotted-decimal / bits in network part
+    split := strings.Split(cidr, "/")
+    dotted := split[0]
+    size, err := strconv.Atoi(split[1])
+    check(err)
+
+    // get IP as binary string
+    var bin []string
+    for _, n := range strings.Split(dotted, ".") {
+        i, err := strconv.Atoi(n)
+        check(err)
+        bin = append(bin, fmt.Sprintf("%08b", i))
+    }
+    binary := strings.Join(bin, "")
+
+    // replace the host part with all zeros
+    binary = binary[0:size] + strings.Repeat("0", 32-size)
+
+    // convert back to dotted-decimal
+    var canon []string
+    for i := 0; i < len(binary); i += 8 {
+        num, err := strconv.ParseInt(binary[i:i+8], 2, 64)
+        check(err)
+        canon = append(canon, fmt.Sprintf("%d", num))
+    }
+
+    // and return
+    return strings.Join(canon, ".") + "/" + split[1]
+}
+
+func main() {
+    tests := []string{
+        "87.70.141.1/22",
+        "36.18.154.103/12",
+        "62.62.197.11/29",
+        "67.137.119.181/4",
+        "161.214.74.21/24",
+        "184.232.176.184/18",
+    }
+
+    for _, test := range tests {
+        fmt.Printf("%-18s -> %s\n", test, canonicalize(test))
+    }
+}