Create 751-ip-to-cidr.js

Author: everthis

751-ip-to-cidr.js

@@ -0,0 +1,21 @@
+/**
+ * @param {string} ip
+ * @param {number} n
+ * @return {string[]}
+ */
+const ipToCIDR = function (ip, n) {
+  const ipToLong = (ip) =>
+    ip.split('.').reduce((acc, x) => 256 * acc + parseInt(x), 0)
+  const longToIp = (long) =>
+    [24, 16, 8, 0].map((i) => (long >>> i) % 256).join('.')
+  const bitLength = (num) => Math.floor(Math.log2(num)) + 1
+  const ans = []
+  let long = ipToLong(ip)
+  while (n) {
+    let mask = Math.max(33 - bitLength(long & -long), 33 - bitLength(n))
+    ans.push(longToIp(long) + '/' + mask)
+    long += 1 << (32 - mask)
+    n -= 1 << (32 - mask)
+  }
+  return ans
+}